In this study, we apply the tripartite decomposition of productivity growth proposed by Kumar and Russell (Amer. Econ. Rev., vol. 92, pp. 527–548, 2002) to estimate and evaluate the contribution of firms’ IT capital accumulation to their productivity growth. Analyzing a panel data on 52 public accounting firms in Taiwan for ten years from 1993 to 2002, our results indicate that the productivity growth of these accounting firms was primarily due to their accumulation of IT capital. In addition, our results indicate that services diversification towards nonaudit services and workforce quality contributed to accounting firms’ IT capital accumulation, which, in turn, led to their productivity growth.