This paper intends to expose the existing relationship between the knowledge organization systems called domain ontologies, in the form of terminological ontologies and classification, more specifically, the archival classification. This research shows a new perspective, since it links studies of knowledge organization in general, focusing on ontologies and classification, and the area of archival science, which has several peculiarities, as will be discussed below. Initially, it was based on the ideas proposed by Madsen and Thomsen in the article Ontologies vs. classification systems (2009), in which the authors expose, in a precise way, how the elaboration of a terminological ontology prior to a classification system can make the system better, more complete and more user friendly. The present work opted for a similar approach, but applied to the archival classification systems, considering that such systems have peculiarities, such as the fact that they have the objective of serving a specific organization and that it has its own administrative body and functions. It is understood here by ontology: a taxonomic organization of the concepts of a certain domain of knowledge, with the attribution of properties to the elements in it, being the terminological ontologies a special kind of this organization system, in which the focus are, as the name itself indicates, the various terms that set a given domain; and by archival classification, it is understood as the way to organize records fiscally and intellectually within a given organization based on its functions and  activities and structure. It is also important to emphasize that classification is a fundamental activity for the work of the archivist, since it is the basis for the accomplishment of the other activities. The present work considered that, starting from the premise that it is possible to understand an organizational environment through a terminological ontology, that is, that the elements of an institution can be treated as concepts of a domain (being the domain the institution itself), also it is possible, therefore, to take this ontology as the basis for the construction of an appropriate classification system to deal with the documents produced in that institution. In order to apply this idea, an ontology was thought based on the existing elements in the organizational structure of an institution, the same on which archival classifications are based: function, fund, type of document, date, confidentiality, etc. From this, all the attributions given to the departments, the functions of each one, and the tasks and both the intermediate and final activities, as well as the records used to achieve the proposed objectives, becomes clear. The classes of the ontology were thought to be the major structural elements of the institution, such as the organizational sectors, while it was considered that the subclasses may be more specific elements of the institution, such as the functions performed by the different sectors, or even more general elements of the archival practice, such as the various types of records (memorandum, letter, circular, ordinance, declaration, edict, etc.). Thus, this ontology allows a deeper understanding of the organization to which the proposed idea is being applied, so that developing the classification of the files can certainly be a somewhat simpler task. In the investigation, it was first tried to take into account all the elements pertinent to an institution, or at least those more common and that represent what an institution is. With this information in hand, it was possible to assemble the terminological ontology. As already mentioned, the classes were formed from the organization's departments, such as administrative, financial, commercial, operational and human resources departments. Subclasses and sub-subclasses were formed based on the functions and activities performed, since the activities are done from certain tasks, performed through specific types of records. With the ontology, developing the classification proved to be a simple task, since all relevant elements were already properly organized, allowing others to be added in the future. The classification was made based on the hierarchical classification model, which allowed some flexibility in the organization of the elements. At the end of the paper, it was concluded that the development of the archival classification system was really improved due to the previous creation of the terminological ontology. This is due to the fact that the ontology allows the archivist to more easily see all the elements of the organizational structure-functions of a given institution without any kind of confusion, as well as to allow expansions in the organizational structure not to be viewed with great difficulty, since this expansion is added to the model of the institution organized through the terminological ontology, the classification system can also be easily adapted. Considering this, two main advantages were found in the application of the proposed idea in relation to the traditional method of archival classification, based only on the description relations between records: the first is in the fact that, having knowledge of the entire organizational structure of the institution through a terminological ontology, it is simpler to see and understand how the institution works and, consequently, to perform the classification; the second is in the adaptability of the developed classification system, since, being the ontology itself is a flexible system, this characteristic is also transmitted to it.