Endometrial receptivity is required for successful implantation and pregnancy. Despite the remaining controversy, many studies have shown that ultrasonographic endometrial thickness can be considered as an indicator of endometrial receptivity.The study objective was to investigate the effect of dilatation and curettage on the endometrial thickness.Enrolled in the study were 444 patients visited in Obstetrics & Gynecology clinic of Shahid Sadoughi hospital between Jan. 2011 to Sep. 2012. Only patients whose menstrual cycle was regular were included in study. Patients with myoma, adenomyosis, endometrial polyps or other uterine anomaly, those who smoked, whose BMI was greater than 30 and who were taking medications that could affect endometrial thickness were excluded. Endometrial thickness was measured one day before evolution (n = 444) and 5-7 days after it (n = 444) using transvaginal ultrasonography. The endometrial thicknesses were correlated to the patients' history of dilatation and curettage. Data analysis was done through SPSS software version 16 and using descriptive statistics, independent T-test and Anova.Endometrial thickness in patients who had 0, 1, 2, 3 and 4 D&C were 10.00 ± 0.58, 9.83 ± 0.47, 8.90 ± 0.92, 7.42 ± 0.18 and 7.40 ± 0.07, respectively one day before ovulation (spearman's correlation coefficient = -0.33) and 10.62 ± 0.68, 9.64 ± 0.49, 8.48 ± 0.96, 6.32 ± 0.15 and 6.90 ± 0.04, respectively, 5-7 days after ovulation (spearman's correlation coefficient = -0.66) estradiol and progesterone levels, measured in the day of 2nd ultrasonography had not statistic relation with endometrial thickness (P = 0.27 and 0.31). The relation of endometrial thickness and age was not significant (P = 0.54 and 0.06).Dilatation and curettage has a significant effect on the endometrial thinning.