This study investigates the impact of minority state capital participation (SCP) on the corporate environmental engagement (CEE) of privately owned firms in China. Analysing 20,133 firm-year observations from 2009 to 2021, we find that SCP significantly increases environmental protection expenditure, improves environmental performance, and elevates ESG ratings. The government's role as a minority shareholder enhances environmental investment capacity and attracts greater external scrutiny from media, the public, and financial analysts, thereby promoting better environmental practices. Crucially, the effect is driven by the state's involvement, as its withdrawal leads to a deterioration in CEE. These findings highlight a potent policy mechanism for advancing corporate sustainability.