This article discusses how human modeling can support social design that aims to solve various social issues by implementing social institutions: new frameworks or new functions of society. Human modeling, which was originally studied for describing and predicting individual performance, has now extended its scope to cover group and social performance by many people. Social design is crucial for our society facing serious problems, but the conventional way of social design, which heavily relies on empirical approaches, is powerless in complicated modern society. It is desirable therefore that more rational and predictive approaches for social design might have been established. Since human performance that affects effectiveness of social institutions is a key factor in social design, human modeling can be a hopeful tool for considering this factor.