Three new nitrogen-containing heterocyclic alkaloids, oryzamutaic acids H–J (1–3), were isolated from the endosperm (polished rice) of an Oryza sativa mutant. The structures and relative stereochemistries of 1–3 were elucidated on the basis of spectroscopic analyses. The presence of three carbons, each bound to a carboxyl group and a nitrogen atom in the structure of 1, suggests that oryzamutaic acids H–J (1–3) are generated from three molecules of a single amino acid.