The objective of this study is to clarify the penetration behavior of spilled oil stranded on sandy beach and to evaluate the effects of the penetrated oil on the infiltration of dissolved and particulate matters by wave action into sandy beach sediments. The penetration depth of stranded crude oil was deeper than that of fuel oil C, which caused by the difference in viscosity between those two oils. Most of the applied oils penetrated into the sediments. Seventy-two percent of crude oil and 98% of fuel oil C in penetrated oil remained in 2cm depth from the surface. The penetrated oil significantly reduced the infiltration of dissolved and particulate matters into the sediments. These results indicate that the penetrated oil prevents the infiltration of both dissolved and particulate matters into the sediments and, therefore, results in the reduction in the supply of oxygen, nutrient, and organic matters for the benthic organisms in the sandy beach.