With special interests to small experimental tank works, we have investigated the tankside wall effects on wave resistance of models. Applying the wave-making theory, we have carried out some numerical works for the series of mathematical models in the following cases. T/L=0.05, 0.10, 0.15, 0.20, ∞; b/L=1/4, 3/8, 1/2, 3/4, 1, 1.5, 2, ∞; F=V/√=0.218-0.707, where L =ship length, T =ship draft, b =water width, V =ship speed. Finally, making use of the image method, we have made towing experiments with single, double and triple models of T / L =0.10. The model length L and tank water width b being 2.333m and 3.500m, the corresponding ratio b / L is 3/2, 3/4, and 1/2 respectively. Comparing the experimental results with theory, we find, unexpectedly large discrepancies that the side-wall effects are more remarkable with the experiments, even in consideration of skin friction augmentations, which may be roughly estimated as 4 and 10 percentages in case of b / L =3/4 and 1/2.