Abstract: Pine wood nematode disease is a most devastating disease of pine trees.In order to make clear the pathogenic mechanism of the disease, under in vitro condition,the activity of benzoic acid(BA) and phenylacetic acid(PA) against the aquacultural excised needles and branches of Pinus massoniana(Pm),Bursaphelenchus xylophilus(Bx) and the diseaserelated bacterial strain GD1(isolated from the body of Bx) and bacterial strain GD2(isolated from the healthy Pm),was determined.The results showed that both BA and PA were toxic to the excised needles and branches of Pm,and the toxicity of BA was stronger.BA of certain concentration(100 μg/mL) could strengthen the vitality of Bx.Both BA of low concentration(10 μg/mL) and PA of higher concentration(100,1 000 μg/mL) could stimulate the reproduction of Bx.PA of low concentration(10 μg/mL) could stimulate the multiplication of GD1.Both BA of high concentration(1 000 μg/mL) and PA of high concentration(1 000 μg/mL) could inhibit the vitality of Bx,and BA had a stronger inhibition activity.BA of high concentration(1 000 μg/mL) could inhibit the reproduction of Bx.Both BA of high concentration(1 000 μg/mL) and PA of higher concentration(100,1 000 μg/mL) could inhibit the multiplication of GD1,while the inhibition activity of both BA and PA against the multiplication of GD2 was stronger than against that of GD1.