Introduction and Objective: Polycystic ovary syndrome (PCOS) is the most common reproductive disorder in women of reproductive age, and overweight and obesity are highly prevalent in women with PCOS. This study aims to explore whether lifestyle intervention can improve gestational weight gain (GWG), glucolipid metabolism, and perinatal outcomes in overweight/obese pregnant women with PCOS. Methods: This study is a randomized controlled trial that included overweight and obese pregnant women with PCOS who met the inclusion criteria of 8–12 gestational weeks. They were randomly allocated to the intervention group and the control group. Women in the intervention group were given individualized counseling on diet and exercise from a trained dietitian and followed up regularly by a trained dietitian. Women in the control group received guidance on diet and exercise in the form of group education. Results: A total of 296 pregnant women were enrolled in the study, including 164 in the intervention group and 132 in the control group. GWG was 11.93 ± 5.67 kg in the intervention group and 11.86 ± 5.35 kg in the control group and did not differ between the 2 groups. According to the per-protocol analyses, women with good compliance had a lower weight gain (10.11 ± 5.56 vs. 12.70 ± 5.31, p = 0.0042). The incidence of gestational diabetes mellitus and other perinatal outcomes did not differ between the 2 groups. For the lipid profile, we did not find significant improvement in the intervention group. Conclusions: Our study showed that lifestyle intervention of diet and exercise did not affect GWG, glucolipid metabolism, and perinatal outcomes of overweight/obese pregnant women with PCOS. However, women with good compliance can benefit from the lifestyle intervention for GWG. We believe that future studies should focus on trial design and increasing compliance to improve the quality of the study.