Two methods of burning wood pellets in a 15 kW boiler were applied. The lo method was based on pellet combustion in the presence of catalysts (V2O5, CuOx, Pt/Al2O3 and Pt) which were directly put on the deflector located in the combustion chamber. The 2nd one was based on co-combustion of the pellets with an active substance (CO(NH2)(2), (C6H10O5)(n), CaO, Na2CO3 and NaCl). In the presence of all used catalysts and active substances, an increase of CO content in the exhaust gases was obsd. relative to the ref. combustion but NOx content was reduced except for urea. In its presence, NOx emission was more than doubled. The best results were obtained for the Pt 0.2 catalyst. A method for combustion in the presence of catalysts has been recommended.