Abstract: Disclosed is a foamable phenolic resin composition comprising, as indispensable components, 100 parts by weight as solids of a resol type phenolic resin, 3 to 100 parts by weight of an acidic curing agent, 1 to 50 parts by weight of a blowing agent, 0.1 to 50 parts by weight of a saccharide and 0.1 to 10 parts by weight of a foam stabilizer, in which a partial or complete acetylation product of a castor oil/ethylene oxide adduct having a hydroxyl value smaller than 15 mg-KOH/g, which is obtained by acetylating a castor oil/ethylene oxide adduct formed by adding 20 to 70 moles of ethylene oxide to 1 mole of castor oil is used as the foam stabilizer and/or a resol type liquid penolic resin obtained by subjecting a phenol and an aldehyde to addition condensation reaction in the presence of a catalyst having a metal ion-forming capacity, in which the residual amount of the catalyst is smaller than 0.