ABSTRACT SIX years of data from erosion plots at Holly Springs, MS, and 10 yr of data from plots at Morris, MN, were used to study variation in soil erodibility through the year. Monthly values of soil erodibility were related to time with a cosine curve. Erodibility varied from a high of 169% of annual average K (K of the Universal Soil Loss Equation) on February 4 to a low of 31% of annual average on August 5 for the Mississippi data. Minnesota erodibility data were described similarly except the maximum and minimum of the erodibility function lagged the Mississippi curve by about 2 months. It was suggested that erodibility could be predicted using a variability function based on normal air temperature data described by a cosine function and average annual K factor values.