The drifting force acting on a three-dimensional body due to waves has some different features with that of the two-dimensional one. With regard to the three-dimensional effect on the drifting force it can be said that firstly the drifting force coefficient C _d reduces because the diffracted waves can scatter in all directions, and secondly due to the motions of the body it can have a maximum which is greater than that of the perfect reflection of waves which were the greatest one in the two-dimensional case. To make sure of the aforesaid point of view, the theoretical calculations of the drifting force coefficient for the prolate spheroid with the ellipticity 0. 5 in beam and/or head sea are carried out, and the results compare favourably with the experimental data. In the beam sea condition the matter is rather similar to the two-dimensional case. However, when the homogeneous spheroid is freely floating in head sea, the coefficient C _d , _free has very high peak 1. 71 near the pitching-resonant frequency, and since the real one is quite a little shifted to the higher frequency side for the model used in the experiment, the corresponding coefficient C * _d , _free shows a tendency to shrink, but yet is still greater than 1. 0. This implies that the drifting force in a three-dimensional body is dominant especially when it is intensely pitching, and if it might be expected to reduce that force, making the moment of inertia small would be an effective way.