In 1951,Bucka and Todd^[1] found that 3-(p-chlorophenyl)-1,1-dimethylurea (CMU) is an outstanding weed killer. It is highly toxic to many plants and possesses long-lasting herbicidal effect in the soil. In 1953,Sharp et al^[2] found that 1,1-dimethyl-3-phenylurea is effective in eradicating deep-rooted perennial weeds in croplands. However,it persists in soil as a sterilant for a shorter period than 3-(p-chlorophenyl)-1,1-dimethylurea. Since the structure of 3-(p-chloro-phenyl)-1,1-dimethylurea is similar to that of CMU, the senior author synthesized and tested it in Nalco^* in 1953 as a herbicide. It was found to be as effective to plants as 3-(p-chlorophenyI)-1,1-dimethylurea. However,it took a longer period for the herbicidal effect.