A simple procedure to determine micro-aggregate stability was developed. The micro-aggregates in aqueous suspension were subjected to controlled energy input imposed by sonic vibration to simulate the breaking down of aggregates by raindrop impact during a rain storm event. The change in aggregate size composition and the consequent increase in clay particle fraction were determined using the laser light scattering technique. Good correlations between soil surface susceptibility to runoff and erosion (as measured with final infiltration rates, soil losses and runoff volumes), spontaneous disintegration as well as disintegration resulting from sonic vibration, were obtained. A quadratic regression model has been proposed.