The methanol solutions of 7-hydroxyquinoline (7-HQ) and 6-methyl-substituted 7-HQ (6-Me-7-HQ) exhibit UV (lambda(max) 370-390 nm) and large Stokes shifted (lambda(max) 510-520 nm) fluorescence spectra. The former and latter were ascribed to the normal (1:1 and 1:2 H-bonded complexes) and tautomer fluorescence spectra. Picosecond fluorescence and nanosecond/picosecond two-step LIF demonstrated that the tautomer fluorescence was generated by the excited-state proton transfer (ESPT) in the 1:2 H-bonded complexes of these compounds. The methanol solution of 7-hydroxy-8-methylquinoline (8-Me-7-HQ) shows a considerably broad UV fluorescence (lambda(max) similar to 400 nm) without the tautomer fluorescence. Concentration dependence (methanol/hexane) of absorption spectra and pK(a) determination of these compounds indicated that 7-HQ and 6-Me-7-HQ probably form 1:2 H-bonded complexes leading to the ESPT, while 8-Me-7-HQ forms only 1:1 H-bonded complex exhibiting no significant ESPT. Taking account of the steric factor of the 6- and 8-methyl groups, the cis conformation of the 7-OH group and the ring nitrogen atom seems to be required for 1:2 H-bonded complex formation leading to the ESPT in alcohol solutions of 7-HQ and its methyl-substituted compounds.