Introduction: Among women with Polycystic Ovarian Syndrome (PCOS), obesity is one of the diagnosis criteria and it is evaluated by waist circumference. We aimed to determine the measurement of waist circumference in women with PCOS. Obesity and PCOS tend to increase throughout the world. In 1994, leptin was discovered to be directly related to body mass index in obesity. Ovarian cystic syndrome has been shown to be associated with leptin levels and also that indicating the need for prevention of obesity in women. Objective: Clinical and medical determination for the waist circumference of women with PCOS and comporation study to leptin and comparative study to leptin levels. Мaterial and Methods: This research included a total of 86 women aged 18-35 in Ulaanbaatar city. We took a permission to start the research at the meeting of the Research Ethics Council of the Mongolian National University of Medical Sciences on March 22, 2019. Statistical analysis of this study results was performed using SPSS 19.0, text recording using Microsoft Office 2018 software, T-test to exclude group differences, ANOVA test for differences between more than two groups, and p<0.05 statistical probability difference. Results: The research of the 56 women tested for leptin in the serum of women with PCOS, 28 (32.5%) had a normal BMI with PCOS and 28 (32.5%) had an excess of BMI with PCOS, respectively. The mean levels of leptin was 13.86±11.40 kg/ml for people with normal BMI, PCOS and 33.78±17.63 kg/ml for people with excess BMI, PCOS. Leptin is higher in women with BMI, PCOS and this result is statistically significant (P-value 0.000). Conclusion Leptin levels are higher during PCOS, and leptin levels increase as the number of risk factors increases. Leptin secretion is affected by BMI and waist circumference.