In this study, the effects of concrete strength and reinforcing clear distance on the damage of reinforced concrete (RC) slabs subjected to contact detonations have been experimentally investigated to establish the design and damage estimation methods of RC shelters. The main results obtained are as follows : 1) The concrete strength and the clear distance don't affect cratering and spalling significantly. 2) The dimensions of the crater and spall are relatively well predicted with the authors' method for the RC slabs with the ultra high strength concrete and much longer reinforcing clear distance than diameters of the crater and spall. 3) The surface and inside cracking tends to occur more remarkably with higher strength concrete and longer reinforcing clear distance.