Drawing on current theories in personality, second-language (L2) oral ability, and psychometrics, this study investigates the extent to which self-consciousness and assertiveness are explanatory variables of L2 oral ability. Three hundred sixty first-year Japanese university students who were studying English as a foreign language participated in the study. Personality was measured with the Japanese version of the NEO-PI-R (Shimonaka, Nakazato, Gondo, & Takayama, 2002), and L2 oral ability was assessed with an institutionalized group oral discussion test in which performances were judged for pronunciation, fluency, grammar, vocabulary, and communication skills. An analysis of covariance structures technique indicated that assertiveness is a significant explanatory variable of L2 oral ability and no effect was found for self-consciousness. Communication skills and fluency were slightly better explained by assertiveness than the other subconstructs of oral ability.