Introduction & Objective: Professionalism is defined as behaviors, goals, or qualities that characterize a profession or a professional person. Teaching professionalism is an essential part of medical residency training. This study aimed to evaluate the level of professionalism and its associated factors in residents in Iran University of Medical Sciences. Materials & Methods: This cross-sectional study included 117 residents from Iran University of Medical Sciences in 2016. The main outcome was professionalism score measured by the Persian validated version of the American Board of Internal Medicine (ABIM) questionnaire. Sex, study field, education grade, and to be familiar with professionalism concept were registered. T-test, ANOVA, and multiple linear regression were used for data analysis. Results: Mean±SD age of the 103 residents was 30.17 ± 2.22 years. The mean ± SD of professionalism and its subscales were 6.1 ± 0.63, 6.35 ± 1.05 for honor/integrity, 6.03 ± 0.9 for altruism/respect, and 5.58 ± 1.38 for excellence, respectively. The results showed that study field (gynecology and neurology) was associated with professionalism (P < 0.05). In addition, it was revealed that being male was a significant factor of higher score of honor/integrity (P = 0.049). Moreover, familiarity with professionalism concept (P < 0.001) and study field (surgery, pediatric, and ear, nose and throat) were associated factors with higher score of excellence. None of the factors had a significant effect on altruism/respect (P > 0.05). Residents’ age was correlated to none of the scale/subscales (P > 0.05). Conclusions: Based on the findings, it could be concluded that to assign professionalism course seems necessary in residency program to enhance the professionalism level in studied population. This study can be an introduction to future researches to distinguish the associated factors with professionalism among different fields.