A steel plate-concrete composite slab system has been widely used in place of conventional reinforced concrete slabs for the reason that they have various advantages such as structural performance, safety and reduction of time and labors in field construction, In this paper, a series of bending fatigue tests was carried out on several types of PSC beams under various cross-sections and loading conditions. The results are as follows: (1)the fatigue failure of PSC beams results from the tensile fracture of bottom steel plate, and (2)fatigue strength of the plate for two million cycles can be estimated at $940kgf/cm^2$ from the S-N curves.