Photochemical properties of p-phenylphenacyl derivatives (PP-X) having C-halide, C-S, and C-O bonds in the lowest (T-1) and higher (T-n) triplet excited states were investigated in solution by using single-color and stepwise two-color two-laser flash photolysis techniques. PP-Xs (X = Br, SH, and SPh) undergo beta-bond dissociation in the lowest singlet excited states (S-1) while the C-X bonds of other PP-Xs are stable upon 266-nm laser photolysis. The T-1(pi,pi*) states of PP-X were efficiently produced during 355-nm laser photolysis of benzophenone as a triplet sensitizer. Triplet PP-Xs deactivate to the ground state without photochemical reactions. Upon 430-nm laser photolysis of the T-1 states of PP-X (X = Br, Cl, SH, SPh, OH, OMe, and OPh), decomposition of PP-X in the T-n states was found. On the basis of the changes in the transient absorption, quantum yields (Phi(dec)) of the decomposition of PP-X in the T-n states were deter-mined, while bond dissociation energies (BDE) of the C-X bonds were calculated by computations. According to the relationship between the Phi(dec) and BDE values, it was shown that the decomposition of PP-X in the T-n state is due to beta-cleavage of the corresponding C-X bond, and that the state energy of the reactive T-n for the C-O bond cleavage differs from that for the C-halide and C-S bond cleavage. The reaction profiles of the C-X bond cleavage of PP-X in the T-n states were discussed.