Students as researchers need valuable resources related to their fields such as theses/ dissertations. Open access should be supported by educational and research institutes and faculty members so that information is easily available to scholars, scientists and students. However, some of the educational and research centers refuse to make their theses and dissertations available, and they announce a variety of reasons for this refusal of access. By identifying these reasons, this research tries to eliminate them. For this purpose, first, according to the results of previous researches, a list of factors influencing open access to theses and dissertations were extracted. Then, in order to complete and finalize the mentioned list, the impact of these factors has been investigated using Delphi method and questionnaire tool. In this research, Delphi panel consists of 14 faculty members of educational and research institutes in Tehran who have been selected by purposeful sampling method. The results show that the factors of laws and regulations, social impact, information technology, author’s credibility, observability, perceived awareness, attitude toward open access, self-confidence in knowledge dissemination, controllability, perceptual compatibility and culture have influence on open access to theses and dissertations.