In order to improve high temperature resistance of phenolic foams, B2O3 were incorporated in it to synthesize boron-modified composites by mold forming and curing. Microstructure of resultant phenolic foams were studied. Effect of boron content on compressive properties and high temperature resistance of phenolic foams were investigated. The results showed that compressive fracture characteristics of boron modified phenolic foams was pseudoplastic. oughness of resin matrix and compressive strength of phenolic foams could be improved by proper amount of B2O3. The compressive strength of PF-4 was best, 10.14 MPa, 5.18 % higher than PF-0. Boron was beneficial to improve high temperature stability of phenolic foams. Thermal decomposition emperature enhanced with increase of B2O3, which went for carbon yield. PF -7 showed better high temperature stability than others, whose thermal decomposition temperature with 10 % weight loss was 447 ℃, 76.68 % higher than that of PF-0, and carbon yield was 66.37% at 800 ℃, 16.05 % higher than that of PF-0.