A footwear system includes at least two uppers of different sizes having respective first sole members which are different in dimension, and a second sole member for attachment to either one of the first sole members. The second sole member is adjustable at least in dimension to be adaptable to dimensions of both of the first sole members and has at least one hollow part whose dimension is changeable for adjustment the second sole member. When the second sole member is attached to one of the first sole members, the hollow part is adjusted to a first width. When the second sole member is attached to the other first sole member, the hollow part is adjusted to a second width different from the first width.