O-Acetylserine (thiol) lyase (OASTL, EC 2.5.1.47) catalyzes the final step in cysteine biosynthesis. The soybean GmOASTL4 gene was overexpressed in tobacco. Transgenic plants showed markedly increased accumulation of transcripts and higher cysteine content compared with the wild-type. Upon exposure to cadmium stress, OASTL activity and cysteine levels increased significantly in transgenic plants. Cadmium accumulation and the activity of both superoxide dismutase and catalase enzymes were enhanced in transformants. These results demonstrate that overexpression of GmOASTL4 in tobacco can enhance cysteine levels and increase tolerance to cadmium stress.