A process for producing a phosphinylamino acid derivative of the formula: ##STR1## wherein R.sup.1 is a lower alkyl group, R.sup.2 is a hydrogen atom, a lower alkyl group, a halo-lower alkyl group or a substituted or unsubstituted phenyl group, and R.sup.3 is a substituted or unsubstituted alkyl group or a substituted or unsubstituted phenyl group, which comprises reacting a compound of the formula: ##STR2## wherein R.sup.1 and R.sup.2 are as defined above, and/or a compound of the formula: ##STR3## wherein R.sup.1 and R.sup.2 are as defined above, with a compound of the formula:R.sup.3 CONH.sub.2 (IV)wherein R.sup.3 is as defined above, carbon monoxide and hydrogen in the presence of a catalyst containing a metal of group VIII of the Periodic Table.