Glutathione synthetase (GS) catalyzes the ATP-dependent synthesis of GSH from γ-glutamylcysteine (γ-Glu-Cys) and glycine. It is predicted that GS-1 is the C. elegans ortholog of GS. To investigate the protective role of cellular GSH against arsenic- and cadmium-induced oxidative stress in C. elegans, we examined the effect of GS-1 in response to arsenic and cadmium exposure. The functional importance of GS-1 in C. elegans is investigated by RNA interference (RNAi) mediated (GS-1-dificent) worms. Under normal growth conditions, pleiotropic phenotypes of GS-1 (RNAi) worms were observed, including shorten life span, decreased survival rate and adult percentage, and morphological changes, suggesting that GS-1 is essential for development and viability. These observed effects were more profound while GS-1 (RNAi) worms were grown in the presence of As (III) and Cd (II), indicating that GS-1 is required C. elegans' defense against As (III) and Cd (II) toxicity. GS-1 mRNA expression regulated by different metals in vivo and in vitro were examined by transgenic C. elegans and real-time RT-PCR analysis. GS-1 mRNA varied in different developmental stages of worms and the highest level of GS-1 mRNA was observed at L4-stage. Heat, paraquat, and Cd (II) significantly induced GS-1 expression with the highest level GFP signal, whereas other metals induced less extent. In this study, our results indicated that GS-1 plays an important role in C. elegans’ development and life span, and it is required for the protection of C. elegans against arsenic- and cadmium-induced oxidative stress.