The active radicals produced from the photolysis of tetra-phenyl-porphyrin(H₂TPP)in benzene have been investigated by spin trapping-ESR technique. The ESR spectrum with 6 lines was detected in the presence of spin trap PBN, it means that spin adduct is [HTPPPBN]^·. The ESR signal with 6 lines was quenched by O₂ and NaI, it can be concluded, therefore, that the photolysis process of H₂TPP was accomplished via triplet excited state.