In this study, an Obihiro City model based on system dynamics was developed to provide a comprehensive assessment of the sustainability of the city, which is emphasized in recent years. Obihiro City was selected as an environmental model city in 2008. Therefore, the city has a feasibility of being a sustainable city. Meanwhile the city faces serious concerns with rapid aging and a very low birthrate. In this study, the sustainability of Obihiro City was evaluated with the following indexes as output indicators of system dynamics. Social indexes ·Low birthrate ·Aging Economical indexes ·Financial capability index ·Work force ratio to population Environmental indexes ·Public transport share ·Food self-sufficiency ·Bioenergy production The city model developed in this study is comprised of three sectors, i.e. the society and population sector, the economic sector, and the environmental sector. The model was developed by considering the relationships among the sectors. The model clarified that aging and a low birthrate will continue. This finding reflects the employment situation of women and a resulting decline in wages. Financial capability index will increase because of the decreasing population. Moreover, the ratio of employees will decrease because of aging and a low birthrate. As for the environmental indicator, the public transport share will decrease in the future. Food self-sufficiency will increase because of a decrease in the population. Bioenergy production will slightly decrease because of agricultural production. JFL Classification: Q01