Activation energies for the swelling of wood in water have been accurately evaluated for the first time. Raising the water temperature above room temperature significantly increased the rate of swelling of wood. Also, an increase in water temperature caused an increase in the maximum equilibrium swelling of wood. It was ascertained once again that a removal of extractives caused an increase in the maximum equilibrium swelling of wood in water. It was also found that removal of extractives caused a large decrease in the swelling activation energy, Ea, for spruce, maple, and aspen