Purpose: The purpose of this study is to assess the amount of changes in the foot size on weight bearing in adult women, which might help in choosing an appropriate size of the shoes. Materials and Methods: The authors measured the length and width of the feet of 200 healthy women on weight bearing and non-weight bearing, and the size of the shoes they wore. Results: Foot length and width differences between right and left sides were 2.53 mm and 2.16 mm respectively on non-weight bearing, and 2.47 mm and 1.77 mm respectively on weight bearing. Foot length and width increased by 2.89% and 7.50% respectively on weight bearing than those on non-weight bearing. Shoe width was 6.82% longer and 9.54% narrower than the weight bearing foot size. There were 25 women who had shoe-related foot pain, all of them wore shoes that were 13.01 % or more narrower than the weight bearing foot width. Foot pain was significantly correlated with the shoe-foot width difference(p=0.0001). Conclusion: The foot size was increased by 2.89% in length and 7.50% in width with weight bearing. The width of their shoes was narrower. than the weight bearing foot width. Shoe-related foot pain was correlated with the foot-shoe width difference.