Highly dimensionally stable particleboards of spruce and Birch were exprimentally made from chips treated with saturated at elevated pressures. The relationships between steam pressure. time of steam treatment and MOR, MOE, IB and thickness swelling, linear expansion of particiebohrds were studied. The results indicated that the optimal technique parameters of steam treating chip were steam pressure: 1.3N/mm~2, steam treating time: 5～6 min, and the stability of the Birch particleboard by steam treated was much greater than spruce.