In this study, the effects of astaxanthin (AST) that belongs to carotenoid family and cadmium (Cd), which is an important heavy metal, on rat erythrocyte G6PD, 6PGD, GR, and TrxR enzyme activities in vivo and on rat erythrocyte 6PGD enzyme activity in vitro were studied. In in vitro studies, 6PGD enzyme was purified from rat erythrocytes with 2',5'-ADP Sepharose4B affinity chromatography. Results showed inhibition of enzyme by Cd at IC50; 346.5 mu M value and increase of 6PGD enzyme activity by AST. In vivo studies showed an increase in G6PD, 6PGD. and GR enzyme activities (P > 0.05) and no chance in TrxR enzyme activity by AST. Cd ion inhibited GbPD, 6PGD, and GR enzyme activities (P < 0.05) and also decreased TrxR enzyme activity (P > 0.05). AST + Cd group G6PD enzyme activity was statistically low compared with control group (P < 0.05). 6PGD and TrxR enzyme activities decreased without statistical significance (P > 0.05); however, GR enzyme activity increased statistically significantly (P < 0.05).