Background and objectives Protein composition analysis of 81 rice samples was performed on three cultivars harvested different regions in Japan, and the effects of the protein composition on the nitrogen composition in sake. Findings Crude protein content showed a significant positive correlation with glutelin content. Yamadanishiki cultivars showed lower crude protein and glutelin contents compared with Gohyakumangoku cultivars harvested from the same field. Total nitrogen content in the enzyme digest of steamed rice grains showed a significant positive correlation with the crude protein and glutelin contents. Ten polished (70%) white rice samples were investigated in a small‐scale sake brewing test. Total nitrogen compounds, bitter‐tasting peptides, and free amino acids in the brewed sake positively correlated with the glutelin content of the rice samples. There were no clear correlations between α‐amylase and acid proteinase activities with the nitrogen compounds in the sake. Conclusions The results indicated that the glutelin content in the cultivar rice affects sake quality through taste‐active and other nitrogen‐containing compounds produced from rice glutelin in the sake brewing process. Significance and novelty We revealed that the glutelin content in the milled rice grains is important to brew high quality of sake clearly. The present results would be useful for cultivation or breeding of sake rice.