Abstract: Objectives. Nickel has been widely used as a constituent of many dental alloys for several decades; however, the potential cytotoxic effects on oral tissues and its mechanism remain undefined. Therefore, the object of this study was to investigate the cytotoxic effect of nickel ions and explore the relationship with oxidative stress. Methods. L929 cells were exposed to different concentrations of nickel ions (0、200、400、800 μM/L）for 24,48 and 72 h, MTT assay was used to assess the cytotoxicity of nickel ions. Cellular oxidative stress was evaluated by intracellular reactive oxygen species (ROS) production and the degree of lipid peroxidation (LPO) indicated by the levels of malondialdehyde (MDA). Results. The results of MTT assay showed that cell viabilities at different culture time points were higher than control, The intracellular ROS production and the content of MDA also increased in dose-dependent manner, which had significant difference to the control (P<0.05). Significance. From these studies, it was shown that cell proliferation of L929 cell was obviously inhibited by nickel ions. Nickel ions may induce intracellular oxidative stress, which maybe one of mechanisms of cytotoxic effect of nickel ions on L929 cells.