Based on the 1991-1993 data of integrated securities firms in Taiwan, this article first uses DEA to assess pure technical, scale, cost and allocative efficiencies of each firm, and then applies the Tobit censored regression model to investigate the determinants of each efficiency measure. The regression results show that firm size has a positive impact on pure technical, scale and cost efficiences. The impacts of a firm's service concentration on pure technical and scale efficiencies are positive, but its impact on allocative efficiency is negative. Firms with a branch or branches are less efficient than those without any branch in terms of pure technical, scale and cost efficiencies. Firms with low operating risks are more efficient than those with high operating risk in terms of cost and allocative efficiencies. Competition pressure forces integrated securities firms to improve their pure technical and cost efficiencies, and shrinks the differences of pure technical efficiency among them in 1993.