Prethrombin-2 recombinantproduction in E. coli still facesa bottle neck due to formation of inclusion bodies. The level of gene transcription can be regulated by using appropriate concentration of IPTG inducer. This study was aimed to determine the effect of isopropyl-β-D-thiogalactopyranoside (IPTG) concentration on prethrombin-2 expression. The prethrombin-2 expression was induced by various concentrations of IPTG at 12^oC hosted by E. coli ER2566. The result show that the suitable IPTG concentration for induction ofprethrombin-2 was 0.010 mM. It was indicated fromthe 63-kDa protein band obtained from the soluble fraction on SDS-PAGE. The higher concentrations of IPTG increased the amount of protein in the insoluble fraction due to the increased of expression rate. It concluded that the IPTG concentration affect the rate ofprethrombin-2 expression.