Although cooperatives are major actors in the transformation of agricultural systems, very little attention has been paid to the conditions that facilitate or hinder their involvement in the sustainable transition. Drawing on theoretical and empirical approaches, we analyze the effect of social capital on the propensity and proportion of investment in environmental assets in the case of agricultural machinery cooperatives (CUMAs) in France. The number of producers within their CUMA is used as a proxy of the bonding social capital and the CUMA's relationships with external organizations as a proxy of the bridging social capital. Our results show a nonmonotonic relationship between the proxies of social capital and investment in environmental assets by CUMAs. However, the effect differs depending on the subdimension of social capital considered. Interestingly, our results show that the effect of social capital within CUMAs remains even when the cooperatives carry out investment renewals that involve less risk for members.