The effect of combustion of biomass on soot aggregates and polynuclear aromatic compounds (PACs) has been studied. Conditions similar to those in typical residential space heating systems used to burn wood have been simulated in a laboratory furnace. The biomass fuels used included (I)paper-mill residue, (2) hard pine-wood, and (3) particle board, typically used in the construction of indoor furniture. Soot formation process was most extensive during the combustion of particle board and hard pine-wood, where the highest combustion temperatures were obtained. It has been found that the effect of temperature/heat input and oxygen/local mixing conditions appear to be important within both the pre-particle chemistry, responsible for the formation of incipient soot particles, and the soot surface-mass growth. The higher combustion temperatures obtained in the wood and board experiments influenced the behavior of PACs. The overall PACs formation tendency decreased in the order: partice board > hard pinewood much greater than paper-mill residue. The experiments have shown that the temperature-time history and C/O ratio are important parameters affecting PACs formation/destruction in biomass combustion.