With　the　development　of　society　and　the　improvement　of　environmental　consciousness,　the　performance　of　corporate　environmental　responsibility　(CER)　has　elicited　increasing　attention　in　recent　years.　In　previous　studies,　the　exploration　of　the　antecedents　of　CER　is　far　less　evident　than　the　exploration　of　its　results,　and　only　few　studies　have　investigated　what　determines　CER　engagement　from　the　perspective　of　supply　chain　concentration　(SCC).　Using　data　from　2413　firms　in　China　from　2013　to　2019,　our　study　uses　the　fixed　effect　model　and　performs　multiple　robustness　tests　to　examine　the　impact　of　SCC　on　the　fulfillment　of　CER,　its　transmission　mechanism,　and　the　moderating　role　of　technology　uncertainty　(TU).　Empirical　results　show　that　SCC　has　a　pivotal　negative　impact　on　CER　performance,　wherein　both　supplier　concentration　(SUP)　and　customer　concentration　(CUS)　are　detrimental　to　CER　performance.　Further　mechanism　analysis　shows　that　such　negative　effect　can　be　explained　by　the　adverse　effect　of　SCC　on　the　operating　cash　flow　(OCF),　in　which　OCF　has　a　partial　mediating　effect.　Moreover,　the　negative　impact　of　SCC　on　CER　performance　is　more　significant　when　the　uncertainty　of　firms＇　technological　environment　is　stronger.　Our　study　opens　the　transmission　＂black　box＂　between　SCC　and　CER　performance　and　incorporates　the　behaviors　of　firms,　inter-firm　relationships,　and　environmental　factors　into　the　same　research　framework,　and　provides　a　theoretical　guidance　for　management　practices.