This study explores the citizens’ attitude towards international collaboration on low carbon development in developing countries through voluntary carbon offsetting, using an experimental social survey in two Japanese large cities. In particular the authors focus on additionality of greenhouse gas emissions reductions through voluntary carbon offset by Kyoto credits generated from climate change mitigation projects in developing countries, providing the respondents of the survey with the opportunity to offset their emissions instead of receiving a gift certificate as remuneration. The study finds around 40% of respondents choose carbon offsetting, of which around half choose carbon offset contributing to the world beyond the Kyoto target of the Japanese government although most of the current Japanese carbon offset providers utilise carbon offset contributing to the Japanese government by means of Kyoto credits. Japanese citizens could conduct more carbon offset using the credits generated from the projects in developing countries, including offset beyond the Kyoto targets, though difficulties in understanding the mechanism of carbon offsetting shall be resolved. Carbon offset providers in Japan and other countries that may have nationally binding target and allow using international carbon offsetting, should consider proving users with both options of offset to meet the national target and offset beyond the national target.