We present a quantum-chemical analysis of the central metal ions effect on first hyperpolarizabilities of a series of push-pull porphyrins whose synthesis and NLO properties has been reported earlier [T.G. Zhang, Y. Zhao, I. Asselberghs, A. Persoons, K. Clays, M.J. Therien, J. Am. Chem. Soc. 127 (2005) 97 10]. The molecular geometries are obtained via B3LYP/6-31G (d, p) level optimization including SCRF/PCM approach, while the dynamic NLO properties are calculated with the ZINDO/CV method including solvent effects. It has been observed that the first hyperpolarizabilities can be greatly enhanced by changing the central metal ions. It is found that the CT transition between the metal ion's d orbital and the macrocycle pi orbital plays an important role on first hyperpolarizability of metal porphyrins. Our data suggest a new approach to enhance nonlinear optical properties of porphyrin materials. (c) 2006 Elsevier B.V. All rights reserved.