Rapid determination of cation exchange capacity (CEC) of soils can be useful for soil testing to improve efficiency of fertilizer use. The methylene blue (MB) method of Wang et al. (1989) has been simplified for rapid determination of CEC of mineral soils in field. For the temperate and tropical soils used, the relationships between the CEC by the ammonium acetate (NH4OAc) method and the simplified MB method were linear (r2= 0.97) with a slope ranging from 0.84 to 1.02. These results suggest that the simplified MB method has the potential for a rapid determination of the CEC of mineral soils.