The paper described the synthesis of a new monomer containing spiro orthoester groups using epoxy resin(E54) and γ butyrolactone with a catalyst of BF3·OEt2. This spiro monomer was used to modify epoxy resin (E44). It was found that the addition of the monomer into epoxy resin system enhanced the conversion of epoxy groups during plymerization in the presence of ethylamine trifluoroborane (BF3·NH2Et). This proved that they could undergo a copolymerization. The adhesive tensile and shear strengthes of the modified epoxy resin increased obviousely as the content of the monomer increased.The above observed phenomena were discussed

and the relationship between shrinkage and adhesive strengthes was investigated.The mechanical properties of the modified epoxy resin matrix were also measured.