Optical switch phenomenon of 7-hydro xyquinoline with excited state proton transfer effect was investigated using pic osecond laser pulses.Experiment results show that 7-hydroxyquinoline could shu t down laser at 488 nm and 632.8 nm under the action of picosecond laser pu lses at 355 nm but nothing happened under the action of picosecond laser pulses at 532 nm.It originates from large nonlinearity of anion and cation formed in ex cited state proton transfer of 7-hydroxyquinoline.