This study tests the theoretical equilibrium described by CAPM(capital asset pricing model) using micro-data from Seoul`s apartment market. Implications of CAPM is derived, and tested for two distinct submakets of Seoul using the methodology proposed by Black, Jensen and Scholes(1972). Returns from individual apartment investment are calculated from monthly apartment price data, and market rates of return are assessed from price indices surveyed by Kookmin Bank. 3 month CD interest rates are used as risk-free rates of return. Our test shows that CAPM is not strictly applicable in the overall market. The result was expected to a certain extent, considering many elements of inefficiency in the real estate market. However, both submarkets show fairly linear relationship between beta coefficients and excess rates of return. It implies that although the broad Seoul housing market differs from what CAPM presumes, individual submarkets may move in a more rational and efficient way.