Two new alkaloids, oryzamutaic acid K and oryzadiamine C, were isolated from the yellow endosperm of an Oryza sativa mutant. The structures of oryzamutaic acid K and oryzadiamine C were elucidated with spectroscopic analyses. Oryzamutaic acid K and oryzadiamine C are new C23N4- and C19N3-type alkaloids, respectively, that possess nitrogen-containing heterocyclic ring systems. Oryzadiamine C may play a significant role in the yellow color of the endosperm. (C) 2020 The Author(s). Published by Elsevier Ltd.