The low speed wave resistance theory developed by Baba⁴⁾ and Maruo⁵⁾ seems to be a promising theory to predict the wave resistance of conventional ships, because it includes the nonlinear effect of the free surface condition. The wave resistance curves calculated by the low speed theory, however, have large humps and hollows, and they do not agree with the measured^{7) 10)} . In this paper, a refinement of the low speed theory is discussed by imposing the more accurate hull surface condition. The wavy source distribution added to satisfy the hull sruface condition is obtained numerically, and the wave resistance, the hull side wave profiles and the velocities around the hull surface are evaluated. The results coincide fairly well with the measured values, especially the humps and the hollows of the calculated wave resistance curves are remarkably reduced. It is ascertained that the added source distribution plays an important role to improve the low speed wave resistance theory, in spite that its strength is one-order smaller than that of the double model source.