Abstract: Phenolic resin was modified by cardanol that replaced part of phenol. The expandable phenolic resol resin was prepared. The influences of the cardanol substitution amount on the properties of phenolic resol resin and phenolic foam were investigated. Using the IR spectra and thermo gravimetric analyzer, the structure and thermal stability of resin were analyzed. The mechanical property was studied by the electronic universal testing machine. The results showed that the resin viscosity was 4 650 mPa·s, free phenolic content decreased from 6.72% to 5.45%, free formaldehyde content decreased from 1.17% to 0.68% and the maximal compressive strength of phenolic foam reached 0.20 MPa when the cardanol substitution amount was 10%. But the thermal stability of phenolic resin and the flame retardant of phenolic foam were reduced.