ABSTRACTProtein quality of cooked milled rice of low‐glutelin (high‐prolamin) content 1 mutant was compared with that of japonica parent Nihonmasari in growing rats. Biological value (BV) of the mutant was lower, but digestible energy and true protein digestibility (TD) were high and similar to those of the parent, resulting in lower net protein utilization of the mutant relative to the parent. Protein of the mutant had lower lysine content than did the protein of the parent, which explains its lower BV, although its prolamin content was lower than that of the parent. Cooking did not adversely reduce TD for both samples, in contrast to earlier studies of japonica and indica rices.