A method for predicting the roll damping of a ship at forward speed is proposed. The roll damping is assumed to be divided into five components, that is, the frictional, the wave making, the eddy making and the lift components of the hull, and the bilge keel one. It is found that the eddy making component of the hull decreases rapidly with forward speed, while the wave making and the lift components increase. The formulas for these three components are deduced from some theoretical considerations and the experimental results. The frictional component is estimated by Kato-Tamiya's method. The bilge keel component is assumed, to be constant at forward speed, and is estimated by the formula which the authors have proposed recently. The values predicted by the present method are in fairly good agreement with the experimental ones for ship models at forward speed.