In order to establish an impact-resistant design procedure for reinforced concrete slabs, the effects of the supporting conditions and thickness of the slab on impact-resistant behavior of the slabs under the consecutive impact loading were experimentally investigated. The supporting conditions considered here are: line supports on four sides, two line supports on two opposite sides, and one line and two corner-point supports. The results obtained from this study were as follows: (1) Even though development of the flexural cracks were affected by the supporting conditions, finally punching shear cracks were formed irrespective of the supporting conditions and magnitude of the slab thickness; (2) the maximum impact force tends to increase according to an increase of the slab thickness; and (3) the case of the line supports on four sides gives the highest impact-resistant capacity for the slab among three kinds of supporting conditions considered here.