Purpose: We investigated the difference of body mass index(BMI) score before and after gonadotropin-releasing hormone agonist (GnRHa) treatment in central precocious puberty girls(CPP). Methods: Medical records of 177 girls with CPP treated with GnRHa were reviewed. All patients completed the therapy. The patients were categorized into two groups according to initial BMI; normal weight group (BMI ˂ 85 percentile) and overweight/obesity group (BMI ≥ 85 percentile). We analyzed chronologic age (CA), bone age (BA), BA advancement (BA-CA), height (Ht), Ht-standard deviation score (Ht_zs), BMI, BMI_zs, predicted adult height ( PAH) before treatment initiation and after treatment completion. Results: Initial CA, BA, Ht_zs, PAH, mid-parental height and the total durations of treatment showed no differences between two groups. But initial BA-CA of the overweight/obesity group was higher than that of the normal group. When comparing the height outcomes of two groups, PAH increased less in the normal weight group than in the overweight/obesity group (ΔPAH = 0.87 vs 3.2, p = 0.029), but there was no correlation between initial BMI_ZS and ΔPAH. ΔBA-CA and ΔHt_zs of two groups were not different. BMI_zs increased only in the normal weight group, and ΔBMI_zs was negatively correlated with initial BMI_zs (r = -0.232, P ˂ 0.001). When the group of patients with increased BMI after the therapy was compared with the group of unchanged BMI, no difference in ΔBA-CA, ΔHt_zs and ΔPAH_zs was found. On multiple regression analysis, ΔBMI_zs was negatively correlated with initial BMI_zs, and it showed no correlation with CA, BA, BA-CA, height. Conclusion: BMI_zs increased after GnRHa treatment in normal weight group, whereas BMI_zs decreased in overweight/obese group. Increment of BMI_zs was negatively correlated with initial BMI_zs.