The damping resistance of roll has been measured from the extinction curve of the free-rolling of a model. But this free-rolling method was hardly applicable to the roll of an angle over20° where free rolling damped immediately. Giving forced oscillations of various amplitudes to a model ship by the newly devised gravity mechanism, and assuming the imput energy of the forced roll equal to the energy dissipated by the damping resistance, the authors have carried out some model experiments to determine the damping coefficients applicable to a large angle where the deck edge of the model was entirely immersed. Fortunately, the authors were able to obtain some satisfying results, and have come to the following conclusions. a) The forced oscillation method is applicable to a roll of large angle, even where the deck edge of the model is immersed, and the extinction coefficient obtained from this method agrees with that which is determined by the free-rolling method. b) The extinction coefficient of roll increases suddenly when the rolling angle exceeds the angle of deck-edge-immersion. c) The extinction curve was found to be approximated by following formula : δθ=λθ ⁿ _m n=1.7 before deck edge immersion n= 3.2 after deck edge immersion where δθ is decreasing angle per swing, θ _m is the corresponding mean angle.