We investigated the effect of membrane toxin 12 (MT-12), isolated from Naja naja atra, a species of Chinese Cobra, on the proliferation and invasion of human bladder cancer EJ cells and studied its mechanisms using MTT assay, Transwell chamber invasion assay, scanning electron microscopy and flow cytometry. The results indicated that MT-12 inhibited the proliferation of bladder cancer cells in a dose-dependent manner. The half maximal inhibitory concentration (IC50) after 72 h was 0.66 µg/ml. The invasion of cells decreased with increasing doses of MT-12 (0.125-0.5 µg/ml, P<0.001). Expression of CXCR4 decreased with the effect of MT-12 for a particular concentration range (0.125-0.5 µg/ml). To conclude, MT-12 is capable of inhibiting the proliferation and invasion of bladder cancer EJ cells. This mechanism may be associated with reduced expression of CXCR4 protein.