Regularities of photoluminescence thermal quenching in micropowder of hexagonal boron nitride were investigated. It was found that integral intensity of 3.56 eV emission band decreases down to background by increasing the temperature from 300 to 750 K. Experimental results were described using Mott-Seitz and Street’s equations, corresponding parameters were evaluated. It was shown that the presence of two non-radiative relaxation channels could cause the observed temperature dependence of the photoluminescence response.