1,3-Oxazin-4-one derivatives represented by general formula (I) ##STR1## wherein R.sup.1 is a lower alkyl group, a lower alkenyl group, an aryl group which may be substituted, or an aralkyl group which may be substituted;R.sup.2 is a hydrogen atom or a lower alkyl group;R.sup.3 is a lower alkyl group, an aryl group which may be substituted, or an aralkyl group which may be substituted; andR.sup.4 and R.sup.5, independently, each is a lower alkyl group, or R.sup.4 and R.sup.5, taken together with the carbon atom to which they are bonded, combine to form a 3- to 8-membered carbocyclic group which may have a branch of a lower alkyl group. These compounds have broad herbicidal spectra and potent herbicidal activities and in addition high safety to useful crops, so that they are useful as herbicides.