The experiment on the effect of fire retardant FR 1 on the hygroscopicity and natural durability of Pinus massoniana and Populus tomentosa was conducted. The hygroscopicity of FR 1 treated wood was less than 28% under high humidity condition, which indicated that anti hygroscopicity of Pinus massoniana treated by FR 1 was much better than that by ammonium phosphate and boron compounds at the different retention. But according to the test results of natural durability of the treated wood, FR 1 was less effective than the preservative CCA or ACQ B, therefore, the author suggested that FR 1 would be not suitable for exterior and ground contact wood.