A new type of unsaturated poly (ester-imide) Viz Phthalic anhydride-ethylene glycol-diethylene glycol - maleic anhydride -urea was prepared by meltpolycondensation. The copolymer was characterized by FT-IR, gel permeation chromatography (GPC) and thermal gravimetric analysis (TGA). Viscosity of the unsaturated poly (ester-imide) was measured with a Ubbelohde viscometer. The molecular structure of the crosslinked unsaturated poly (ester-imide) was determined by wide angle X-ray diffraction. The mechanical properties with different heat treatment conditions are investigated. Hydrolyzed in 1 M NaOH standard solution at room temperature to study the crosslinked unsaturated poly (ester-imide) mass loss at different heat treatment conditions and crosslinker content. All the preliminary results suggested that the copolymer might be potentially used as bone fixation materials.