The purpose of the present study was to examine the social projection effect concerning the strength of national attitudes. Japanese respondents sampled from the general population judged how patriotic and nationalistic opinions were distributed among Japanese (i.e. in‐group) and American (out‐group) citizens. The respondents’ own positions regarding these attitude dimensions were also measured. As predicted, the respondents inflated estimates of the endorsement for positions close to their own, particularly when the target was the in‐group. Estimates of opinion distributions in the out‐group converged around stereotypic positions. The apparent projection effect in patriotism (i.e. in‐group liking) was likely mediated by abstract trait evaluations of the home country, while the projection of nationalism (i.e. ethnocentrism) appeared to be a direct result of projection without such mediation. Different processes such as the motivation for cognitive consistency and the need to achieve social identity of the group were suggested to underlie projection effects in different domains. Implications of the results for the study of stereotyping and intergroup conflict are discussed.