An electron donating polymer including moiety A represented by Chemical Formula 1, and a solar cell including the electron donating polymer are provided. In Chemical Formula 1, X1 is a functional group including at least two ester residual groups and a substituted or unsubstituted divalent aliphatic organic group linking the ester residual groups, and X2 is one of hydrogen, a halogen atom, a substituted or unsubstituted C1 to C20 aliphatic group, a hydroxy group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C1 to C30 ketone group, a substituted or unsubstituted C1 to C20 ester group, a thiol group, —SR100 (wherein R100 is one of a substituted or unsubstituted C1 to C20 aliphatic group, a substituted or unsubstituted C2 to C30 aromatic group, and a substituted or unsubstituted C2 to C30 heterocycloalkyl group), and a combination thereof.