The function of foliar betacyanin as a photoprotective mechanism in water stressed Amaranthus cruentus plants was examined by comparing leaves of two strains differing significantly in betacyanin accumulation. Drought treatment was imposed by withholding irrigation for 2 days and at 0, 1, and 2 days after treatment onset, leaves were subjected to high light (HL) treatment to assess their tolerability to photoinhibition. The drought treatment reduced relative water content and gas exchange rate to similar extent in both strains. As drought developed, the extent of photoinhibition after HL treatment increased in both strains, however, it was significantly greater in acyanic than in betacyanic strains, indicating higher tolerance of betacyanic leaves to photoinhibition. The betacyanic leaves also exhibited higher values for quantum yield of PSII (ΦPSII) and photochemical quenching (qP) during drought treatment despite the non-photochemical quenching (qN) did not differ between strains. These results may be partially explained by light screening effect of foliar betacyanin. Moreover, the increased betacyanin and decreased chlorophyll contents in betacyanic leaves were thought to have enhanced effectiveness of photoprotection provided by betacyanin during the drought period. Our results demonstrated the potential protective function of foliar betacyanin against photoinhibition in A. cruentus under drought conditions.