9,10-Dihydroxybenzo[ℎ]quinoline (1), a 10-hydroxybenzo[ℎ]quinoline (2) derivative, was synthesized and characterized by 1H NMR, 13C NMR, UV-vis and fluorescence spectra, and single-crystal X-ray diffraction. Compound 1 possesses an intramolecular six-membered-ring hydrogen bond, from which excitedstate intramolecular proton transfer (ESIPT) takes place from the phenolic proton to the pyridinic nitrogen, resulting in a proton-transfer tautomer emission of 650 nm in dichloromethane. Its molecular geometry in the ground state has also been calculated using density functional theory (DFT) at the B3LYP/6-31G∗∗ level and compared with its crystal structure. Results show that the optimized geometry can well reproduce the crystal structure. Furthermore, both absorption and emission spectra of 1 and 2 were calculated using time-dependent DFT (TD-DFT) calculations, and were in good agreement with the experimental results.