A series of aluminum complexes supported by $eta$-ketoamino, ligand-bearing, 3-position substituents $LAlEt_2$ ($L=CH_3C(O)C(Cl)=C(CH_3)NAr;(L_1)$, $L=CH_3C(O)C(H)=C(CH_3)NAr;(L_2)$, $L=CH_3C(O)C(Ph)=C(CH_3)NAr;(L_3)$, and $L=CH_3C(O)C(Me)=C(CH_3)NAr;(L_4)$, $Ar=2,6-^iPr_2C6H_3$) were synthesized in situ and employed in the ring-opening polymerization (ROP) of $varepsilon$-caprolactone ($varepsilon$-CL) and cyclohexene oxide (CHO). The 3-position substituents on the $eta$-ketoamino ligand backbone of the aluminum complexes influenced the catalyst activity remarkably for both ROP of $varepsilon$-CL and CHO. Aluminum $eta$-ketoamino complexes displayed different catalytic behavior in ROP of $varepsilon$-CL and CHO. The order of the catalytic activity of $LAlEt_2$ was $L_1AlEt_2$>$L_2AlEt_2$>$L_3AlEt_2$>$L_4AlEt_2$ for ROP of $varepsilon$-CL, being opposite to the electron-donating ability of the 3-position substituents on the $eta$-ketoamino ligand, while the order of the catalytic activity for ROP of CHO was $L_1AlEt_2$>$L_3AlEt_2$>$L_4AlEt_2$>$L_2AlEt_2$. The effects of reaction temperature and time on the ROP were also investigated for both $varepsilon$-CL and CHO.