Soil erosion from fields located in the hilly lands of Shikoku was investigated. These are the areas where agricultural practices are quite limited and fields are often left idle and unutilized. Based on the results of the investigation, the calculated soil loss in terraced paddy fields and upland fields was about 3 t ha^-1y^-1 and 8 t ha^-1y^-1, respectively. Large soil loss (about 90 t ha^-1y^-1) was calculated to occur within several years immediately after abandoning cultivation of fields. Though soil loss did not largely increase in fields which changed to mowed grass fields (about 12 t ha^-1y^-1), there was a significant increase in mowed grass fields which changed to wild fields (about 40 t ha^-1y^-1). Soil loss in wild fields which were not cultivated for more than 6 years, decreased and became relatively stable (about 10 t ha^-1y^-1). To estimate the potential soil erosion of abandoned fields which are no longer cultivated, the Universal Soil Loss Equation (USLE) was revised to create the Hilly-land Soil Loss Equation (HSLE) by the addition of a term related to the erosion caused by intrusive surface and shallow-underground water runoff.