The work is to investigate α-particle irradiation-induced bystander effects on the mutagenicity in human chromosome 11 in the human−hamster hybrid (A,L, cells) and its possible mechanism. A,L, cells were used for assaying mutation rates of human chromosome 11 through screening mutants in the presence of anti−CD59 surface antigen antibody (S1) and complement. A grid was interposed between α−particle source and the cells being irradiated, so as to fix proportion of the irradiated cells (15 %) and the bystander effects on the mutagenicity were detected. Free radical scavenger DMSO and intercellular communication inhibitor Lindane were selected to investigate the potential mechanism of α−particle induced bystander effect. There was clear dose−dependent relationship between mutation rate and the dose of alpha particle radiation. However, the mutant fractions of cell population shielded by the grid in α−particle irradiation system were much higher than the expected levels of irradiated cells. Lindane, but not DMSO, could obviously decrease this bystander effect induced by α−particle irradiation. Alpha−particle irradiation can induce bystander effect on the mutagenicity, in which intercellular communication may play important roles.