Aggregates of two tropical soils from Western Nigeria were used to investigate the possibility of using the raindrop technique to determine the soil erodibility index as compared with soil behavior towards erosion under natural field conditions. Aggregate size, initial soil moisture potential, and raindrop temperature were tested for their effect on structural stability of the soils. High soil moisture potential (more negative) significantly increased the erodibility of a clayey soil containing expanding lattice clay minerals. The erodibility index of a sandy clay loam soil containing kaolinitic clay minerals and amorphous iron and aluminium oxides was slightly decreased when at high moisture potential. The increase in water temperature increased the erodibility of both soils. Erodibility was found to vary directly with sand and inversely with clay content. A routine laboratory method of evaluating the erodibility of a soil using a rating curve is proposed.