Unsaturated polyester poly(fumaric-co-itaconic-co-butanediol) (poly(FA-co-IA-co-BD)) was prepared with fumaric acid (FA), itaconic acid (IA), and 1,4-butanediol (BD) by melt polycondensation, and its self-cross-linking kinetics was investigated through the percentage of insoluble gel fraction (Q_s) and conversion degree of C=C (DC). The results showed that poly(FA-co-IA-co-BD) had the highest Q_s and DC, when the mole ratio of FA and IA was 1:0.96, which meant that the polyester had the maximum extent of self-cross-linking. And the polyester had the maximum rate constant (k) and the smallest activation energy (E_a). The value of k was temperature dependent, and the higher the temperature, the higher the value of k. Thermodynamics parameters such as <img src="1.tif">, <img src="2.tif">, and <img src="3.tif"> were also discussed. The results showed that, <img src="1.tif"> > 0, the self-cross-linking reaction of the poly(FA-co-IA-co-BD) occurred at high temperature. The self-cross-linking reaction was an exothermic reaction, <img src="2.tif"> was equivalent to E_a. <img src="3.tif"> < 0, the product in the transition state was more ordered. When the mole ratio of FA to IA was 1:0.96, poly(FA-co- IA-co-BD) was the most ordered in the transition state and had the smallest <img src="3.tif">, and the C=C in the polyester self-cross-linked easily.