Structures of enactins Ia, Ib₁, Ib₂ and Va were determined by spectroscopic studies using their bis-2, 4-dinitrophenyl derivatives. Both enactins and neoenactins contain L-serine to form the hydroxamic acid structure. Their physico-chemical and biological properties are closely related. The structures of neoenactin congeners have been previosuly reported and enactins Ia and Va are proved to be 19-hydroxyneoenactin B₂ and 14-dihydroneoenactin M₁, respectively. Both enactins Ib₁ and Ib₂ are determined to be 19-hydroxyneoenactin B₁ and considered to be diastereoisomers at the 19-position, though their steric structures at this positioin remain to be determined.