Lack of sufficient interest among western psychologist in blood type theories of personality has left the topic to be influenced by traditional belief. This paper shows that although this belief is widespread in Japan, where research findings do not support a relationship between blood types and personality traits, western evolutionary psychologists have given a new dimension to it by linking blood types with evolution of human civilization and dietary practices. Future research on relationship between blood type and personality needs to consider individuals’ expectation, prejudice, and attitude to discrimination.