Pure, 0.1, 0.5 and 1 mol% Tm-doped YAP single crystalline scintillators were grown by the μ-PD method. Lattice constants were gradually decreased with Tm concentration in XRD analysis. In transmittance measurement, absorption bands due to Tm3+ 4f-4f transitions were observed at 265, 360, 485, 690 and 800 nm and they were ascribed to the transition from the 3H6 ground state to its excited states, 1I 6, 1D2, 1G4, 3F3 and 3H4, respectively. Strong emission peak due to 1I6-3F4 transition of Tm3+ was shown at 350 nm under X-ray irradiation. Photoluminescence decay time constants caused by this transition were evaluated to be from 15.3 to 17.3 μs and the scintillation decay time constants under gamma-ray excitation were estimated to be from 17.5 to 18.8 μs. Tm 1% doped one exhibited the highest light yield of 15100 ± 1500 photons/MeV when excited by 137Cs gamma-ray irradiation.