The discontinuity of the institutional initiatives oriented to the documentary preservation in format microfilm in Argentina has prevented the coordinated development of projects of microfilmation. With the objective to know and to spread to the historical documentation in format microfilm lodged in Argentine and foreign institutions, as well as to systematize the particular initiatives in this field, the Historical Training center and Information Park of Spain (Rosary, Argentina) it undertook the accomplishment of the Project of Census of Documentary Archives in Microfilm format. The article refers the objectives, criteria of organization, development and results of this Census, in which approximately 300 institutions participated. The processed information includes the bibliographical description of the collections, the physical description of microfilms and the conditions of storage of masters, catalogued according to the parameters established by format MARC for this type of material.