OBJECTIVE To investigate the effects of different concentrations of indium chloride (InCl3) on the proliferation of human lung epithelial (Beas-2B) cells and its potential mechanism. METHODS Beas-2B cells were exposed to different concentrations of InCl3 (0.3, 1.0, 3.0, 10.0, 30.0, 90.0, 270.0, and 810.0 µmol/L) for 24, 48, and 72 h, respectively. The effects of InCl3 on cell proliferation were determined by the CCK-8 assay. The effects of InCl3 on apoptosis were evaluated using annexin V-PI staining followed by flow cytometry. The level of intracellular reactive oxygen species (ROS) in Beas-2B cells after exposure to InCl3 was determined using 2', 7'-dichlorofluorescein diacetate labeling followed by flow cytometry. RESULTS Compared with the control group, InCl3 at a relatively low concentration (0.3~3.0 µmol/L) significantly promoted cell proliferation (P < 0.05), while InCl3 at a relatively high concentration (30.0~80.0 µmol/L) significantly inhibited cell proliferation after 72 h (P < 0.05). InCl3 at a concentration of 0.3 µmol/L failed to induce apoptosis within 72 h; however, InCl3 at a concentration of 30.0 or 810.0 µmol/L induced substantial early apoptosis after 72 h. Compared with the control group, cells exposed to 0.3 µmol/L InCl3 showed a slight decrease in the level of intracellular ROS within 72 h, while cells exposed to 30.0 or 810.0 µmol/L InCl3 showed a significant increase in the level of intracellular ROS after 72 h (P < 0.05). CONCLUSION At a low concentration, InCl3 stimulates cell proliferation by reducing intracellular ROS. However, at a high concentration, InCl3 inhibits cell viability by elevating intracellular ROS and inducing apoptosis.