Background and objectives: The objective of this study was to determine the extent to which differences in rice grain protein composition are associated with head rice yield (HRY). HRY, the mass of milled unbroken rice grain derived from a defined mass of paddy rice expressed as a percentage, is a commercially important trait targeted by rice breeders. Variation in rice grain protein composition influences rice grain texture, and high grain protein content is associated with high HRY; however, the relationship between rice grain protein composition and HRY is not well understood. Findings: HPLC analysis of protein extracts derived from broken and unbroken milled medium- and long-grain rice suggests that rice grain protein composition differences are associated with HRY. Glutelin, a major class of rice grain storage proteins, displayed the greatest difference between broken and unbroken rice grains but weakest association with HRY. Prolamin and globulin content displayed relatively smaller differences between broken and unbroken medium and long grains, yet both protein fractions were associated with HRY. Conclusions: Rice grain protein composition, in addition to other known factors, influences rice HRY. Significance and novelty: Protein composition differences between broken and unbroken rice grains have significant implications for human nutrition and in part explain differences in HRY. Rice breeders face the challenge of balancing the two competing traits of HRY and soft grain texture.