Glucose-6-phosphate dehydrogenase (G6PD) is the first enzyme on which the pentose phosphate pathway was checked. In this study, purification of a G6PD enzyme was carried out by using rat erythrocytes with a specific activity of 13.7EU/mg and a yield of 67.7 and 155.6-fold by using 2,5-ADP Sepharose-4B affinity column chromatography. For the purpose of identifying the purity of enzyme and molecular mass of the subunit, a sodium dodecyl sulfate-polyacrylamide gel electrophoresis was carried out. The molecular mass of subunit was calculated 56.5kDa approximately. Then, an investigation was carried out regarding the inhibitory effects caused by various metal ions (Fe2+, Pb2+, Cd2+, Ag+, and Zn2+) on G6PD enzyme activities, as per Beutler method at 340nm under in vitro conditions. Lineweaver-Burk diagrams were used for estimation of the IC50 and K-i values for the metals. K-i values for Pb+2, Cd+2, Ag+, and Zn+2 were 113.3, 215.2, 19.4, and 474.7M, respectively.