Abstract: Objective: To investigate inhibitory effects of arsenic trioxide(As₂O₃) on the growth of B₁₆ cell solid tumours in C57BL/6J mice and telomerase activity;and to provid experiment basis for treatment of malignant melanoma.Methods: Mouse melanoma B₁₆ cells were transplanted into C57BL/6J mice that were treated with different concentrations of As₂O₃.The weight of tumor and percent of tumor development were examined.The telomerase activity in mice tumours was detected by TRAP-PAGE-silver staining.Results: The tumor growth was significantly inhibited by As₂O₃.The microvessel density in tumor tissues was obviously reduced by As₂O₃(P<0.01).Treated with As₂O₃,the telomerase activity was obviously reduced.Conclusions: As₂O₃ can inhibit the growth and the telomerase activiy of B₁₆ cell solid tumours in C57BL/J mice.