A quantitive analysis on tannin contents of 7 kinds of wooden materials and their wafer extractives was given in this study. The results indicated that there are no significant relationship between, the tannin contents from water extractires of the wooden materials and setting of gypsum slurry as the strength of gypsum prism, although the hydrolyzable tannins can retarded the hydration of gypsum slurry severely. In addition, a result obtained from a experiment of manufacturing gypsum-bonded particlehoard made from populus showed that 80% of commercial retarder Retardan P can be replaced by the water, extractives-from oak barks.