This paper examines the impact of cross-ownership on the strategic incentive of environmental corporate social responsibility (ECSR) within a green managerial delegation contract in a triopoly market engaged in price competition. It demonstrates that bilateral cross-ownership between insiders provides weak incentives to undertake ECSR, which has a non-monotone relationship with cross-ownership shares, while it provides strong incentives for outsiders, which increases the ECSR level as cross-ownership increases. It also compares unilateral cross-ownership and finds that a firm that owns shares in its rival has a greater incentive to undertake ECSR than its partially-owned rival, while an outsider has more incentive than firms in bilateral scenarios. These findings reveal that a firm's incentive to increase a market price through ECSR critically depends on its cross-ownership share, while it decreases environmental damage and increases social welfare when the environmental damage is serious.