Purpose: Cluster analysis on pediatric asthma identifying a cluster characterized by obesity, females, and puberty showed that obe-sity is an independent risk factor for severe asthma in this cluster. In the present study, we aimed to investigate the effect of over-weight/obesity on lung function and asthma severity in prepubertal asthmatic children. Methods: One hundred fifty-five prepubertal children (aged 6-10) with asthma were enrolled and divided into 2 groups: the over-weight/obese group (body mass index [BMI] ≥85th percentile, n=44) and the normal BMI group (<85th percentile, n=111). We re-viewed their medical records and analyzed whether there were any differences in clinical features, lung function and degree of bron-chial hyperresponsiveness (BHR) between the 2 groups. The clinical factors associated with asthma severity were also investigated. Results: There was no difference in clinical features between the 2 groups. Pulmonary function tests showed that only forced vital capacity in 1 second/forced vital capacity (FEV1/FVC) was significantly lower in the overweight/obese group than in the normal BMI group (P=0.032). There was no difference in dysanapsis and BHR between the 2 groups. There were significantly more children with moderate-to-severe asthma in the overweight/obese group compared to the normal BMI group (P=0.018). In multivariate logistic regression analysis, overweight/obesity has been identified as an independent risk factor of affecting asthma severity (odds ratio, 2.44; P=0.018), in addition to the already known risk factor, FEV1. Conclusion: Our study showed that overweight/obese prepubertal asthmatic children had lower FEV1/FVC than those with normal BMI. It also suggests that overweight/obesity may be an independent risk factor for severe asthma before puberty. (Allergy Asthma Respir Dis 2021;9:231-237)