Objective (s): Organizational culture is the shared beliefs and values ​​of the employees, which determine their attitudes, norms, feelings, habits and behaviors. Organizational culture has a great influence on hospital performance. This study aimed to measure the organizational culture of hospitals affiliated to Tehran University of Medical Sciences. Methods: This descriptive and cross-sectional questionnaire survey was conducted in 14 hospitals of Tehran University of Medical Sciences in 2020. A researcher-made questionnaire including 48 items in two dimensions of internal coherence and external adaptation and 4 components of teamwork, accountability, risk-taking and responsiveness was used to measure the organizational culture of hospitals. The questionnaire was designed specifically for healthcare organizations. The questionnaire determines four types of organizational culture of indifference, conservative, market and excellence for hospitals. The questionnaire was completed by 600 managers and employees. SPSS statistical software version 22 was used for data analysis. Results: The average score of organizational culture of hospitals affiliated to Tehran University of Medical Sciences was 2.76 out of 5 points. The average score of internal coherence and external adaptation dimensions of organizational culture were 2.69 and 2.82; The average score of the components of teamwork, accountability, risk-taking and responsiveness were 2.52, 2.87, 2.46, and 3.18; and the average scores of the levels of beliefs, values, behaviors and symbols of organizational culture were 2.81, 2.86, 2.56 and 2.79 out of 5 points, respectively. Thirteen hospitals had an excellent culture and one hospital had a market culture. The average score of organizational culture in specialty hospitals was higher than in general hospitals (p<0.05). Conclusion: Hospital managers should promote the organizational culture by strengthening the internal coherence dimension of the organizational culture and the components of teamwork and accountability. Also, measures should be taken to strengthen the levels of values ​​and beliefs of the organizational culture.