The photophysical properties of ortho-Cl, meta-Cl and para-Cl substituted tetraphenylporphy-rin-histidine and their zinc (Ⅱ) complexes have been studied by means of steady-state absorption and fluo-rescence spectroscopies, as well as time-resolved fluo-rescence spectroscopy. For the cases of both free-base and zinc complexes, it was found that the or-tho-chlorine substitution onto the phenyl rings signifi-cantly altered the fluorescence quantum yield, the fluorescence lifetime and the ratio between radiative and nonradiative deactivation rates of the porphyrin chromophore, i.e. the photophysical parameters werequite different from those of meta- and para-substi-tuted compounds. On the other hand, however, theintroduction of covalently-linked histidine did not ex-ert much effects on the photophysical behavior of the porphyrin chromophore. The results are interpreted in terms of the steric effect and the heavy-atom effect from the chlorine atoms substituted onto the phenylrings. The photophysical properties of ortho-Cl, meta-Cl and para-Cl substituted tetraphenylporphy-rin-histidine and their zinc (II) complexes have been studied by means of steady-state absorption and fluo- rescence spectroscopies, as well as time-resolved fluo-rescence spectroscopy. For the cases of both free-base and zinc complexes, it was found that the or-tho-chlorine substitution onto the phenyl rings signifi-cantly altered the fluorescence quantum yield, the fluorescence lifetime and the ratios between radiative and nonradiative deactivation rates of the porphyrin chromophore, ie the photophysical parameters were quite different from those of meta- and para-substi-tuted compounds. On the other hand, however, the introduction of covalently-linked histidine did not ex-ert much effects on the photophysical behavior of the porphyrin chromophore. The results are interpreted in terms of the steric effect and the heavy-atom effect from the chlorine atoms substituted onto the phenylrings.