Objectives The purpose of this study is to investigate the safety and effect of Biman-tang (BMT) on two different administration periods in the treatment of childhood overweight and obesity. Methods In retrospective study, 39 overweight and obese ($85^{th}$ percentile ${leq}$ Body Mass Index (BMI)) children were treated with BMT from January 2006 to April 2013 at Korean Medical Clinic in Suwon, Korea. The primary outcomes were the changes in BMI and Obesity Index (OI) from baseline to the treatment groups. Secondary outcomes included the changes in height, weight and safety of the medicine. Comparisons of BMI, OI, height and weight between the short-period (SP) treatment group and the long-period (LP) treatment group were done by using ANCOVA. Results The change of the mean of BMI ($-0.5{pm}0.6kg/m^2$ vs $-1.4{pm}0.8kg/m^2$, respectively; p=0.003) and OI ($-3.6{pm}3.9%$ vs $-9.7{pm}4.7%$, respectively; p<0.001) showed significant reduction both in SP (n=16) and LP treatment group (n=23). The mean height showed no significant difference in both groups. The mean weight of LP treatment group showed significant reduction compared to SP treatment group ($-0.2{pm}1.3kg$ vs $-1.6{pm}1.6kg$, respectively; p=0.006). Most of the children were compliant to the medication and no serious adverse events were found in two groups. Conclusions These findings emphasize that BMT is effective in the treatment of childhood obesity and it requires at least 45 days of treatment for the best result.