A process for preparing lactamide with a high conversion and a high selectivity without the deterioration of a catalytic activity in a short time, which comprises subjecting lactonitrile to a hydrating reaction in the presence of (A) a catalyst including an oxide of manganese as a main component, (B) an oxidizing agent and (C) hydrogen cyanide or hydrogen cyanide and a compound represented by the formula ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are each a hydrogen atom, a C.sub.1 to C.sub.8 alkyl group, a C.sub.1 to C.sub.8 hyroxyalkyl group, a C.sub.1 to C.sub.8 aminoalkyl group or a C.sub.1 to C.sub.8 halogenoalkyl group.