This　study　aims　to　explore　the　effects　of　corporate　environmental　responsibility　on　firms　that　partner　with　NGOs.　On　the　basis　of　the　contrasting　mechanisms　of　needs　and　opportunities　for　legitimacy　seeking,　we　propose　an　inverted　U-shaped　relationship　between　a　firm＇s　environmental　responsibility　and　its　propensity　to　form　partnerships　with　NGOs,　and　the　contingent　effect　of　political　ties.　Empirical　analyses　of　cross-sector　partnerships　between　private　firms　and　NGOs　in　China　provide　support　for　the　hypotheses.　Our　study　emphasizes　the　importance　of　a　firm＇s　environmental　responsibility　in　forming　collaborative　ties　with　NGOs,　and　offers　new　insights　on　the　dual　role　of　legitimacy　in　organizational　partnerships.