Background: The present study aims to examine the effect of estrogen level between volleyball player's and sedentary women' endometrial thickness with regular exercise. Materials and Methods: Seventeen athletes taking place in the 3rd Turkish Women Volleyball League and 17 sedentary women participated in this study. The mean age of athletes was 20.70 +/- 2.11 and sedentaries 21.70 +/- 0.77 years has been identified. In the period between 10 and 11 days of their menstrual cycle, 2 cc venous blood was taken from the subjects. Data calculation was done using the SPSS 21 statistical package program. Descriptive statistics included the arithmetic averages of data and standard deviations (SD) and the error level of p < 0.05 was considered to be significant. Results: No statistically significant relation was found between the sports and sedentary women's mean age and BMI values (age: p 0.076, BMI: p = 0.134 and p > 0.05). No significant differences were found between the two groups' estradiol and endometrial thicknesses (estradiol: endometrial thicknesses: p = 0.01 and p < 0.05). Conclusions: The results showed that the average thickness of the endometrium and estrogen levels of athletes are lower than in sedentaries, and these results indicate that sports may have a preventive effect against uterine cancer and endometrial thickening.