We here investigated and reported the effects of beer drinking on radiation-induced chromosome aberrations in blood lymphocytes. Human blood that was collected either before or after drinking a 700 ml beer was in vitro irradiated with 200 kVp X rays or 50 keV/μm carbon ions. The relation between the radiation dose and the aberration frequencies (fragments and dicentrics) was significantly (p < 0.05) lower for lymphocytes collected 3 h after beer drinking than those before drinking. Fitting the dose response to a linear quadratic model showed that the alpha term of carbon ions was significantly (p < 0.05) decreased by beer drinking. A decrease of dicentric formation was detected as early as 0.5 h after beer drinking, and lasted not shorter than 4.5 h. The mitotic index of lymphocytes was higher after beer drinking than before, indicating that a division delay would not be responsible for the low aberrations induced by beer drinking. An in vitro treatment of normal lymphocytes with 0.1 M ethanol, which corresponded to a concentration of 6-times higher than the maximum ethanol concentration in the blood after beer drinking, reduced the dicentric formation caused by X-ray irradiation, but not by carbonion irradiation. The beer-induced reduction of dicentric formation was not affected by serum. It is concluded that beer could contain non-ethanol elements that reduce the chromosome damage of lymphocytes induced by high-LET radiation.