Working memory (WM) capacity refers to the ability to keep information in the brain for a short period of time. It is said to be a strong predictor of future academic performance. Previous studies have suggested that WM capacity correlates with some brain regions such as inferior frontal gyrus (IFG) in healthy adults. Studies on adults' brain have shown relationships between WM and inferior frontal gyrus (IFG). However, relationships between WM and brain structure in healthy children are still unclear. Terefore the purpose of this study was to investigate the relationship between WM and brain structure in healthy children using large size of cross-sectional brain MRI. The participants of this study were 264 right-handed healthy Japanese children and adolescents (5-to-15 years old). We acquired T1-weighted images and WM capacity from the subjects. WM group index of WISC-3 was used as a WM capacity. We conducted voxel-based morphometry (VBM) in analyzed the correlation between brain structure and WM capacity. Then we analyzed the correlation between regional grey matter volume (rGMV) and WM capacity using multiple regression analysis, in which age and sex were used as covariates. As a result, we found a significant positive correlation between WM capacity and the rGMV in the left IFG with small volume correction (FWE. P<0.05). Although previous studies have pointed out that children do not use frontal regions efficiently for several higher cognitive functions such as executive functions due to prematuration of these regions, our results suggest that WM capacity is related with the frontal brain regions in healthy children.