The aim of the study was to evaluate and explain the performance of professors supervising doctoral theses of doctoral students. The research method was mixed and using an explanatory design. In the quantitative part, the descriptive method was used. The statistical population consisted of professors at Allameh Tabatabaei University who supervised at least one doctoral thesis in the academic years (1402-1399) and doctoral students who defended their thesis in the same period. Available individuals were selected as the sample. 120 doctoral students responded to a questionnaire on the obligations and duties of a supervisor. Data analysis using a paired t-test showed that the performance of supervisors in the process of supervising doctoral dissertations from the students' perspective was significantly lower than the desired level in the entire scale and its components. Grounded theory was used to explain these results. Fourteen supervisors were selected purposefully and semi-structured interviews were conducted with them. The text of the interviews was analyzed using open, axial, and selective coding, and 60 open codes and 7 axial codes (participation and constructive interaction between professor and student, personality characteristics and responsibility of professors, characteristics of the thesis topic, support and accompaniment of students, multiplicity of disciplines and different inputs, improvement of the quality of doctoral theses) were extracted, and a systematic theoretical model was developed to accurately and comprehensively explain the obligations and missions of supervisors, which, if used, will increase the quality of theses and help solve the problems of society.