Nonresonant exponential amplification of the excited-state intramolecular proton transfer (ESIPT) emission has been investigated with the film of ESIPT dendrimer (QG2) by pico- and femtosecond laser experiments. The intrinsic four-level nature of ESIPT and the reduced concentration quenching by dendritic effect made QG2 film an optical gain medium with the threshold intensity lower than 20 muJ/cm(2)/pulse. The characteristics of emission amplification are discussed in terms of the amplified spontaneous emission (ASE) related with ESIPT.