Stepwise photocleavage of naphthylmethyl-oxygen (C-O) bonds of mono(substituted-methyl)naphthalenes [1- and 2-ROCH2Np, R = 4-benzoylphenyl (BP), phenyl (Ph), and methyl (CH3)] and bis(substituted-methyl)naphthalenes [1,8-(ROCH2)(2)Np and 1,4-(ROCH2)(2)Np, R = BP and Ph] was observed to give the naphthylmethyl radicals (NpCH2center dot or ROCH2NpCH2center dot) in almost 100 % yield with two-step or three-step excitation by the two-color two-laser or three-color three-laser irradiation, respectively, at room temperature. The C-O bond cleavage quantum yields of 1-PhOCH2Np, 2-PhOCH2Np, 1,8-(PhOCH2)(2)Np, and 1,4-(PhOCH2)(2)Np were higher than those of 1-BPOCH2Np, 2-BPOCH2Np, 1,8-(BPOCH2)(2)Np, and 1,4-(BPOCH2)(2)Np. No C-O bond cleavage occurred from 1,8-(HOCH2)(2)Np and 2-CH3OCH2Np in the higher triplet excited state (T-n). The experimental results show that the C-O bond cleavage was determined not only by the position of the substituents on Np but also by the type of the substituents. The C-O bond cleavage of 1-ROCH2Np was more efficient than that of 2-ROCH2Np. In the case of 1,8-(ROCH2)(2)Np and 1,4-(ROCH2)(2)Np. (R = BP and Ph), the first C-O bond cleavage from the T-n states occurred to give ROCH2-substituted naphthylmethyl radicals (1,8- and 1,4-ROCH2-NpCH2center dot) when the T-1 states, generated with the 308-nm first laser irradiation, were excited using the 430-nm second laser. The second C-O bond cleavage occurred when 1,8- and 1,4-ROCH2NpCH2center dot in the ground state [1,8- and 1,4-ROCH2NpCH2center dot(D-n)] were excited to the excited states [1,8-and 1,4-ROCH2NpCH2center dot(D-n)] using the third 355-nm laser during the three-color three-laser flash photolysis at room temperature. It was revealed that acenaphthene was produced as the final product during the stepwise C-O bond cleavages of 18-(BPOCH2)(2)Np and 1,8-(PhOCH2)(2)Np. This is a successful example of stepwise cleavage of two equivalent C-O bonds in a molecule using the three-color three-laser photolysis method.