It is important to evaluate the health effects of radiation concurrent exposure to chemicals in our daily life. Myosmine, an alkaloid in tobacco plants and various edibles and staple foods, has been considered as a co-genotoxic agent in vitro. In the present study, the damage induced by radiation concurrent exposure to myosmine was assessed in human primary cell line AG1522. Myosmine at 5 or 10 mM for 3 h treatment induced a significantly dose-dependent increase in micronucleus (MN) frequencies, but not for 1 mM. However, 1 mM myosmine distinctly enhanced MN frequencies in both irradiated and non-irradiated bystander regions after different doses (0.2, 1 and 10 cGy) of alpha-particle irradiation. Treatment with c-PTIO, a nitric oxide (NO) scavenger, the induced fractions of MN frequencies were dramatically inhibited both in 1 cGy alpha-particle irradiated and non-irradiated bystander regions with or without myosmine treatment. Moreover, 1mM myosmine treatment distinctly enhanced gamma-H2AX foci formation in both 1 cGy alpha-particle irradiated and non-irradiated bystander regions. These data indicated that myosmine effectively enhanced the low dose alpha-particle-induced DNA damage in both irradiated and non-irradiated bystander regions and nitric oxide played a very important role in such process.