The level of intellectual identity of a discipline is assessed by its capacity for establishing theories. The main objective of this research is defined as to examine the use of theory in the library and information science in Turkey. The sample of the research consists of 366 graduate theses, which are listed in the HEC National Thesis Center database and completed in the departments of Information Management between 1983-2019, with permission to access their content (n=366). The subjects of the theses, the names of the theories used in the theses, the level of the use of theory, and their scientific origin were examined by the content analysis method. According to the findings, 75 theories are mentioned in the theses, and at least one theory is referred in 22% of the theses. Theses on the subject of user studies and library / information centers are used theories the most. Bertalanffy's general systems theory, Wilson's information behavior theory, and document life cycle theory are the most widely used theories in the theses. The degree of theory use indicates 2.6 in the five-point ratio scale of the Five Degrees of Theory Use Model. 58.6% of the theories used in these theses are related to social sciences, and 30.6% of them are about the library and information science. The majority of social science-based theories belong to the disciplines of psychology and management.