The paper represent a theoretical attempt to investigate the role that the local government can play in improving the level of social capital for the development of industrial districts. The social capital is not, as generally suggested by the socio-economic literature, an individual attitude towards something which does not imply privately appropriable economic benefits, as it is for a pure public good (which would not imply privately appropriable benefits). Social capital should be interpreted as a public component of an investment which implies private and public benefits entangled with each other. Firms could not have sufficient incentive to increase its investment in social capital, because this investment strictly depends on the economic convenience of investing in the impure public good. Starting from this point of view, we underline the importance of investing local public resources (funds, time and effort) for the development of the local social capital.