Background : Increasing physical activity plays an important role in the promotion of the quality of life of women with polycystic ovarian syndrome (PCOS). This study examined the impact of a theory- informed behavior change techniques intervention in conjunction with a pedometer-based intervention on physical activity and weight of women with PCOS. Method : This research is an unmasked controlled trial study. 88 women with PCOS referred to Mahdieh hospital Tehran, Iran and met the inclusion criteria were assigned by random assignment method to the intervention (12-week pedometer-based intervention plus a theory- informed behavior change intervention) and the comparison (12-week pedometer-based intervention) group. The primary outcome was physical activity that was measured in two ways. Step-counts were measured using pedometer, and self-reported physical activity was measured via the international physical activity questionnaire. The secondary outcomes were predisposing, enabling, and reinforcing factors that were measured through a psychometric self-administered questionnaire. Weight was also measured as a secondary outcome. All outcomes were measured at baseline and after 12 weeks. Data were analyzed using STATA software version 13. Data analysis was performed on an intention to treat basis using Independent T-Test, ANOVA ANCOVA test, Repeated Measure ANOVA, and post-hoc analysis. Results : After adjusted mean, significant increases with a strong and moderate effect size were found in the intervention group relative to the comparison group for step-counts (P= 0.000, d = 2.01), walking (P=0.000, d=0.92), predisposing factors (P=0.000, d=1.05), enabling and reinforcing factors (P <0.05, d= 0.54 - 0.60). Significant decrease was found in the intervention group compared to the comparison group for weight (P=0.005) with a moderate effect size (d = 0.66). Conclusion : This pedometer-based intervention that applied behavior change techniques on the basis of predisposing, enabling, and reinforcing factors of the PRECEDE framework was affective to enhance physical activity and diminish the weight of women with PCOS. Therefore, it is suggested to incorporate theory- informed behavior change techniques into pedometer-based interventions for promoting physical activity. Trial registration : Iranian Registry of Clinical Trials IRCT20161116030923N3. Keywords: Physical activity, Polycystic Ovarian Syndrome, Theoretical framework, Behavior change techniques, Pedometer