This paper aims to grasp the current state of social capital and its relations to civic activities and environmental sustainability in Japan. The authors present findings from the first comprehensive survey designed to measure social capital, conducted in 2003, with the focus on civic activities in Japan, together with three cases relating to sustainable environmentalism. The major findings of the survey were: (i) each component of social capital and voluntary and nonprofit activities has a positive correlation, (ii) social capital has changed over time, and (iii) social capital exhibits major city-rural and regional gaps in Japan. Over time, trust and associations with neighbours and relatives have declined, while trust and associations with colleagues at work have been stable or even increased. Some implications are suggested concerning the roles of citizens, nonprofits, government and business: citizens and nonprofits play a crucial role in creating social capital, and government and business can play a facilitator role in the formation of social capital. Moreover, utilization of social capital through partnerships among different sectors is vital for vibrant communities and environmental sustainability.