Upconversion emission properties of gamma-AlON:Yb3+,Tm3+ phosphors were investigated under single-wavelength diode laser excitation of 980 nm. Blue (479 nm) and red (653 nm) emission bands were observed which correspond to the transitions of (1)G(4)-> H-3(6) and (1)G(4)-> F-3(4) of Tm3+ ions, respectively. The upconversion spectra show a concentration-dependent luminescence intensity, reaching its peak at a concentration of 1.2 mol% Yb and 0.5 mol% Tm. Pump power dependence of the upconversion emission intensity (P-I) revealed that a two-photon process was involved in the blue and red emissions.