The effects of understories and their litter covers on sustaining large infiltration rates were studied through rainfall simulator experiments having large kinematic energies (2, 210 J/s/m²). Chloroethylene rectangular containers were packed to a uniform bulk density with A-layer soil. The soil, which were collected from two experimental plots underlain by Granite and Paleozoic sedimen-tary rocks in the Suzuka Mountains, were sieved by a 4-mm sieve and air dried. Five kinds of vegetation were planted and three kinds of litter covered the soil in the containers. The experimental results showed that the infiltration rate is proportional to the canopy coverage of Granite soil, having a great susceptibility to crust formation. In contrast, the infiltration rate was related to the unit leaf area, having little susceptibility to crust formation. The results indicate that understories prevent the forming surface crust, and the effect is greater when the leaf size is larger.