Objective To assess the safety and effectiveness of ketogenic diet on improving polycystic ovary syndrome (PCOS) ⁃related symptoms in patients with overweight or obesity. Methods According to the inclusion and exclusion criteria, 18 PCOS patients were recruited in our study from December 2018 to May 2019, and were all carried out ketogenic diet intervention alone. The duration was one month for 8 patients and two months for the other 10 patients. All recruiters were followed up every day and rechecked monthly while the safety and effectiveness indexes were observed in the course. Results Of the eighteen patients who were treated with a ketogenic diet for one month, the body weight［（75.03±9.17）kg vs（69.64±8.74）kg］, fat mass ［（27.10±6.95)kg vs (23.22±7.05）kg］, BMI［（28.01±4.13)kg/m2 vs (25.99±3.90）kg/m2］, body fat rate［(35.68%±5.09%）vs （32.84%±6.11%)］, testosterone［(0.64±0.19)ng/ml vs (0.54±0.16)ng/ml］, LH/FSH［(1.74±1.03） vs （1.19±0.85)］ and fasting glucose［(5.36±0.81)mmol/L vs (4.62±0.53)mmol/L］were decreased dramatically. Of the ten patients who were treated with a ketogenic diet for two month, the body weight［（73.09±6.44)kg vs (65.35±5.58）kg］, fat mass［（25.54±4.99)kg vs（20.30±5.17）kg］, BMI［（27.21±2.95)kg/m2 vs (24.33±2.55) kg/m2］, body fat rate［(34.76%±4.64%) vs (30.77%±6.04%)］, and fasting glucose ［(5.40±0.92)mmol/L vs (4.61±0.55)mmol/L］were decreased dramatically. The median menstrual cycle decreased from 60 days to 44 days among the ten patients, which was statistically significant. The incidence of grade I adverse reactions during ketogenic diet treatment was 22.2%, mainly constipation, fatigue and hyperuricemia, which were significantly improved after rest and diet modification. Conclusion This Preliminary studies suggested that ketogenic diet intervention may be one of the safe and effective ways of body quality management for PCOS patients, and can normalize the menstrual cycle of PCOS patients.