The purpose of this study was to investigate the effects of body mass index on fundamental motor skills performance in 7-8-year-old boys in Hamedan. Forthis purpose, 72 elementary students were selected via cluster randomization from the elementary schools of Hamedan and divided into three groups: fat, normal, and thin according to percentile diagram. Then, TGMD-2 was performed by children and data were analyzed via K-S, Leven test and ANOVA. The results indicated a significant difference in hop, broad jump and over arm throw and no difference in run and catch subscales. The post hoc test indicated that the normal group performed hop, broad jump and over arm throw better than fat group. In addition, thin group performed broad jump and over arm throw better than fat group. Presumably, the inverse relationship between high body mass index basic motor skills relate to mechanical and recognition factors, components of movement, moving body mass, component coordination and motion range.