A series of unsaturated polyesters (UP) based on succinic acid, adipic acid, sebacic acid, maleic anhydride, ethylene glycol, dieth-ylcnc glycol, triethylene glycol. and propylene glycol were prepared. The molecular weights of the prepared UP were determined via end group analysis. The prepared polyesters were crosslinked and their mechanical properties were measured. Sty-rene (Sty) and Sty/acrylonitrile (AN) mixtures were utilized as crosslinkers. The effect of the structure of the resins on their curing and mechanical behavior has been investigated. On the basis of the experimental results, we concluded that the flexibility increases with increasing molecular weight of the dibasic acid and increasing AN content in the monomer mixture. It has been found also, that the embodiment of PG seems to enhance the rigidity of the cured resin.