The present study explored the influences of subjective and descriptive norms on environmentally conscious behaviours between the USA and Japan. It was predicted that subjective norms would have a larger effect on behaviour in Japan than in the USA. Descriptive norms were expected to have a greater influence on behaviour in the USA. The survey was done with 160 American students and 114 Japanese students. The results showed that subjective norms are relevant only in Japan, but the effect was limited. Alternatively, descriptive norms were a powerful determinant in the USA. It was also found that respondents asserted that they commit environmentally conscious behaviours more frequently than others, regardless of their country. The present research suggests that the role of subjective and descriptive norms may vary between cultures, and highlights a necessity for distinguishing between interpersonal and social norms.