This study seeks to understand the impact of different ownership structures on carbon emissions. We use data from listed firms in Japan, where the government requires firms to disclose the volume of carbon they emit. Our empirical findings are summarized as follows. First, the cross-sectional analysis reveals that firms with foreign institutional investors tend to emit less CO2. In contrast, we do not find evidence that domestic institutional investors reduce carbon emissions. The results are robust under various alternative estimations, such as firm-fixed effects, propensity score matching, and IV (instrumental variable) estimation; they are also robust when the enactment of Principal Responsible Investment (PRI) by the United Nations is included as an exogenous shock. While various studies have examined the factors affecting a firm’s carbon emissions, few studies examine the influence of its ownership structure. We focus on firm ownership structure, especially ownership by institutional investors, because of their substantial impact on managerial decision-making.