A series of unsaturated polyesters (UP) based on phthalic anhydride (PHA), succinic acid (SU), adipic acid (AD), sebacic acid (SE),maleic anhydride (MA), ethylene glycol (EG), diethylene glycol (DG), triethylene glycol (TG), and styrene (Sty) were prepared. The molecular weights of the prepared polyesters were determined by the end group analysis. The effect of the structure of the resin on its mechanical and curing behavior has been investigated. On the basis of the experimental study, we concluded : (1) the maximum curing temperature, T-max, is related to the molecular weight of the glycol incorporated in these castings. In this context, T-max. was found to decrease with increasing the molecular weight. Meanwhile, the time to peak temperature, t(max), was increasing; (2) the values of T-max, Young’s modulus and compressive strength were found to be influenced to a large extent with the type of the saturated acid as well as the molecular weight of the glycol embodied in these resins. A relation representing the variation of compressive strength, sigma(u), as a function of equivalent polymerizable double bonds, EPDB, was derived. It was assumed that this equation can be used to predict the compressive strength for any particular UP formula from its theoretical EPDB value.