Novel diphenylurea derivatives represented by the following formula (I): ##STR1## wherein R.sub.1 is an alkyl group of 5 to 18 carbon atoms, each of R.sub.2 and R.sub.3 is independently an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms or a halogen atom, R.sub.4 is hydrogen atom, an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms or a halogen atom, and X is oxygen atom or sulfur atom, are provided. The compounds are potent in reducing the cholesterol level in serum, and useful for treating hyperlipemia and atherosclerosis.