Succinic acid was presented as a small molecule low shrinkage additive (LSA) in unsaturated polyester resin (UPR). The effects of succinic acid on the volume shrinkage and the flexural strength of UPR cured at 80 6 1 C were investigated and compared with those of macromolecule LSAs, including polyvinyl acetate (PVAc), polymethyl methacrylate (PMMA), and polystyrene (PS). The results indicated that the volume shrinkage of succinic acid/UPR specimen was significantly lower than those of specimens with macromolecule LSAs. The flexural strength of succinic acid/UPR specimen was improved. The optimal time of pre-esterification between succinic acid and the excess dihydric alcohol in UPR was 3.0 h, and the optimal addition of succinic acid was 20 g per 100 g UPR. Compared with 2,2-dimethyl malonic acid we put forward before, succinic acid was a cheaper and more commercial LSA, which obviously accelerated the pre-esterification process and presented excellent antishrinkage effect. DSC showed that with the addition of succinic acid, the polymerization of UPR was distinctive. The two-stage polymerization of UPR glue including the crosspolymerization of UPR and the homopolymerization of polyester was changed to a one-stage polymerization with lower exotherm and slower polymerization rate, which was optimal for UPR. FTIR and high resolution magic angle spinning nuclear magnetic resonance (HR/MAS NMR) were applied for the quantitative characterization of pre-esterification caused by succinic acid. Succinic acid performed better effects on the polymerization of UPR as compared to previous LSAs, and finally the homogeneous micro-structure of cured succinic acid/UPR formed and was demonstrated by SEM.