The Glutathione S-transferase (GST, EC.18.104.22.168) catalyzes the conjugation of hydrophobic compounds inc- luding electrophilic centre to the glutathione (GSH). In this study, purification of GST from bonito liver for the first time and examination of some metal ions’ effects on enzyme activity were aimed. Purification procedure was performed in two steps as preparation of homogenate and glutathione-agarose affinity chromatography. The purity of enzyme was controlled by SDS-PAGE, and it exhibited two bands. It was found as heterodimer structure. Additionally, effects of some metal ions were examined on the enzyme activity. For metal ions showing inhibitory effects, IC50 values were calculated by Activity% [metal ion] graphs and Ki constants and inhibition types were determined via Lineweaver-Burk graphs. Pb2+, Cr2+ and Fe3+ ions had not any effects on the enzyme activity. Yet, while Co2+ activated the enzyme, Ag+, Cu2+, Cd2+ and Zn2+ showed inhibitory effect. Inhibitory order was found as Cu2+>Ag+>Cd2+>Zn2+ with the K values of 0.166 ± 0.046 μM; 0.0146±0.0047 mM; 0.0883±0.0335 mM and 1.39±0.44 i mM respectively and enzyme was inhibited noncompetitively by these metals.