Novel 2-oxo-imidazolidine derivative of the formula: ##STR1## wherein R.sup.1 is lower alkyl or phenyl-lower alkyl, R.sup.2 is lower alkyl, R.sup.3 is alkyl of one to 12 carbon atoms or phenyl-lower alkyl and R.sup.4 is hydrogen or lower alkyl, and a pharmaceutically acceptable salts thereof are disclsoed. Said compounds (I) and salts thereof are useful as hypotensive agents.