Abstract: The main objective of this study was to evaluate the effects of polymeric betaine (PB) on the fire retardant performance of oriented strand board(OSB) treated with 12% of boric acid-borax (1∶1). The panels were produced with phenol formaldehyde resin. The fire retardant performance of OSB was studied by cone calorimeter. The flammability parameters, including average heat releasing rate (av-HRR), total heat release (THR), average mass loss rate (MLR), total smoke release (TSP) and average specific extinction area ( av-SEA) were recorded simultaneously. The results showed that most combustion parameters of OSB decreased by the treatment. Especially for the OSB treated with PB and boric acid- borax, the av-SEA and TSP decreased dramatically ,which indicated a synergistic effect between PB and boric-acid-borax in OSB. Meanwhile, the formation of charcoal was promoted with the presence of PB.