h-BN nanowalls obtained from B3N3H6-NH3 were stable in the Ar atmosphere up to 1100 °C. A reaction with O2 in the Ar atmosphere led to forming of oxidized h-BNO nanowalls. Annealing in dry air resulted in degradation and complete evaporation of the samples. Luminescent properties of h-BN nanowalls can be improved by inert annealing at 1100 °C.