We study the ligand effect on the LUMO/HOMO of ligated zinc porphyrin (ZnP) by utilizing DFT. The ligated ZnPs are zinc meso-tetraphenylporhyrin (ZnTPP), zinc tetrabenzoporphyrin (ZnTBP), zinc meso-tetraphenyltetrabenzoporphyrin (ZnTPTBP) and five-coordination ZnTPP with imidazole (ZnTPP(Im)). The ligands decrease LUMO-HOMO energy gap (ΔEg) of ligated ZnPs with respect to non-ligated ZnP, which is in good agreement with experiments. LUMO of ZnTPP and ZnTBP is stabilized by LUMO+1 (b1-type, C2v-symmetry) of respected ligands, while their HOMO is destabilized by HOMO -4 (a1, C2v) and HOMO (a2, C2v) of respected ligands. DE of ZnTPP and ZnTBP can be adjusted by changing the ligand's electronegativity, such as halogen substitution at the ligands. Halogenated ZnTPP has DE°Csmaller than ZnTPP, which con- firms the experiments. Geometry change in ZnP, which allows the intermolecular perturbation in the frontiers molecular orbitals, shifts LUMO/HOMO energies as it is shown for ZnTPP(Im) and ZnTPTBP. The calculated ΔEgof ZnTPP(Im) and ZnTPTBP are greater than that of ZnTPP and ZnTBP.