Sex difference in susceptibility to oral infection with Corynebacterium (C.) kutscheri was experimentally studied in ICR mice. Immature (4-week-old) and adult (14-week-old) mice were inoculated with two infecting doses of C. kutscheri, and necropsied for bacteriological and serological survey 4 weeks after the bacterial infection. No macroscopic lesions at necropsy were demonstrated, except for one adult male given 10⁹ bacteria. In immature mice, C. kutscheri isolated from the oral cavity and cecum with FNC agar, were recovered in only 40.0% of female mice but in 90.0% of male mice given 10⁶ bacteria (p<0.05), and in only 55.6% of female mice but in 80.0% male mice given 10⁸ bacteria. In adult mice given 10⁹ bacteria, the organism were recovered in only 45.5% of female mice but in 90.9% of male mice (p<0.05), furthermore, the mean number of organisms in the cecum of male mice harboring the organism was significantly higher than that in females (p<0.01). Castration caused an increase in host resistance in adult male mice. These results indicated that ICR male mice were more susceptible than females, in terms of bacterial colonization in the cecum and the oral cavity, to oral infection with C. kutscheri.