Poly (L-lactic acid) (PLA) /starch blends with various starch content were made by injection molding. The blends were exposed to soil and the degradation behaviors were investigated in detail. The test piece of PLA (starch Owt %) did not decompose after 30 days. On the other hand, the blends (starch lOwt % and 30wt %) discolored, and cracks appeared on the surface. The degradation was prominent for higher starch content. For starch Owt % (pure PLA) and 10wt %, the molecular weights of PLA in the samples slightly decreased with exposure time. For 30wt %, on the other hand, the molecular weight decreased rapidly. The number of microorganisms in 30wt % sample was much larger than that in lOwt % sample. These results suggested that the presence of starch enhanced the multiplication of microorganisms, resulting in the acceleration of degradation of PLA in the sample.