Emission formation during thermal conversion of biomass fuels at different conditions has been the scope of this study. The experiments were conducted in a quartz glass reactor where the temperature and atmosphere can be adjusted. The fuels were selected accurately in order to cover a wide range of biomass/waste compositions. They are torrefied softwood, spruce bark, waste wood, miscanthus, and wheat straw. The fuels were first grinded and then pressed into pellets of the same size and weight with a pellet maker. Each pellet was about 200 mg. The experiments were performed under combustion and pyrolysis condition, with atmosphere of 3 % O-2 and 100 % N-2, respectively. Each fuel was combusted under temperatures of 800, 900, and 1,050 degrees C. O-2 and the formed SO2, NO, CO and CO2 were monitored by three analysers. The fuel pellet was kept under combustion and pyrolysis at four residence times. The residue weight was measured after each process and the comparison with the ash content of the original fuel is made. Time dependent formation of NO and SO2 and other emissions is presented and discussed in this paper. Effect of temperature and combustion condition is also considered for the conclusion.