Objectives: To evaluate sexual function in Iranian pregnant women in different trimesters. Materials and methods: This cross sectional study was conducted in a women's hospital between August 2013 and August 2014. Four hundred pregnant women were asked to answer the valid and reliable Persian version of Beck depression inventory (BDI) and valid FSFI (Female sexual function index) questionnaires. Results: Forty five subjects were in the first trimester of pregnancy, 170 in the second trimester and 185 in the third trimester. Except BDI and desire subscale of FSFI, all scores were significantly different between the three groups. By considering 26.55 as the cut off point for FSFI, 38 (84.4%) women in the first trimester, 138 (81.2%) in the second trimester, and 156 (84.3%) in the third trimester had sexual dysfunction. Logistic regression analysis showed that BDI was an independent predictor of sexual dysfunction among participants. Conclusions: As sexual life is an important aspect of marital life, physicians should pay more attention to it in pregnant women.