This　paper　considers　a　supply　chain　with　a　manufacturer　(M)　and　two　retailers　(R1　and　R2).　To　investigate　the　effects　of　R1’s　corporate　social　responsibility　(CSR)　level　on　emission　reduction　cooperation,　four　cooperation　modes　are　discussed.　The　results　show　that　R1　can　use　CSR　as　a　strategic　tool　to　obtain　competitive　advantages,　strengthen　his　cooperation　with　M　and　prevent　cooperation　of　M　and　R2　under　certain　conditions.　The　increase　of　R1’s　CSR　level　enhances　the　emission　reduction　level　and　consumer　surplus,　while　its　impact　on　channel　members’　profits　depends　on　the　emission　reduction　cost.　A　side-payment　contract　is　proposed　to　motivate　channel　members　to　participate　in　cooperation.　Under　this　contract,　the　profit　improvement　rate　for　the　manufacturer　initially　reduces　and　then　enhances　as　R1’s　CSR　level　increases.　Moreover,　the　research　is　extended　to　the　case　that　the　retailers’　products　are　imperfect　substitutes　and　thus　indicates　that　channel　members’　mode　preferences　are　affected　not　only　by　product　homogeneity　but　also　by　R1’s　CSR　level.　©　The　Author(s),　under　exclusive　licence　to　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature　2025.