According to the definition of the fiber-saturation point made by Tiemann,the phase tran-sition between sorbed water and water vapor in wcod is studied here by means of the thermody-namical theories on phase transition in equilibrium. An equation of moisture content of wood atfiber-saturation point is derived form the conditions for phase transition in equilibrium. In thispaper,a calculation is carried out for the moisture content of sitka spruce specimen at fiber-satu-ration point and the calculated values are coi...