The influence of wood extractiveson the hydration and the bending strength of gypsum plaster and gypsum-bonded particleboard was examined under the existence of commercial retarder RETARDAN P Results indicate: 1. wood extractives can retard the hardening of gypsum plaster and gypsum particleboard, and the bonding strength is also declined Wood species and the quality of gypsum also play important roles for the degree of influence; 2. wood extractives can reinforce the retarding effect of RETAR-DAN P. Meantime the setting time of gypsum .particieboard can be predicted by that of gypsum plaster under interaction of both; 3. the bending strength of gypsum particleboard depends on the wood species, but does not evidently on the addition of retarder.