Novel caged phosphate esters were synthesized. Flame-retardant mechanism of poly(vinyl chloride) (PVC) blends plasticized with these synthesized caged phosphate esters was investigated with limiting oxygen index (LOI), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and cone calorimeter tests. The results showed that caged phosphate esters improved the thermal stabilities of PVC blends: LOI values of PVC blends increased from 24.2% to 35.9%, peak heat release rate decreased from 379.04 to 258.79 kw m(-2), and total smoke increased from 1877.9 to 3698.1 m(2) m(-2); hence, the flame retardancy of PVC blends was improved.