The photoconductive properties of a mesogenic long-chain tetraphenylporphyrin, 5,10,15,20-tetrakis(4-n-pentadecylphenyl)porphinatooxovanadium(IV) were investigated and compared with those of the metal-free compound for a symmetrical sandwich-type ITO cell. This compound shows two types of lamellar mesophases (M-LC and M-L phases) and the phase transition sequence is Cr 51 M-LC 83 M-L 140 Iso. A similar photocurrent rectification behavior to the corresponding metal-free tetraphenylporphyrin mesogen was shown. However, the observed photocurrent was remarkably larger than that of the metal-free compound for all phases. The action spectra and the temperature dependence of the dark- and photocurrents were also investigated on the mesomorphic phase transition behavior. These results imply that the photoconductive property of mesogenic tetraphenylporphyrin-based compounds could be drastically affected by a change of molecular fluctuation and long-range order through mesomorphic phase transitions and a metal species inserted in the central core.