Lanthanum cyanurate was synthesized by reacting cyanuric acid and lanthanum nitrate at basic condition and was characterized by elemental analysis and Fourier transform infrared spectroscopy. Its application as thermal stabilizer for poly(vinyl chloride) (PVC) was investigated by Congo red test and discoloration test. In comparison with other heat stabilizers, including lanthanum stearate, calcium stearate, and zinc stearate, lanthanum cyanurate exhibits high stabilizing effect with excellent initial color of PVC. The stability time reaches the maximum (80 min) when the percentage of lanthanum cyanurate in PVC is 2.5%. The combination stabilizers (LaC3N3O3/Zn(St)(2) obviously increase the complete discoloration time of PVC in comparison with the stabilizer of Zn(St)(2). The stability time of PVC increases from 14 min (stabilized by zinc stearate) to 26 min (stabilized by LaC3N3O3/Zn(St)(2)). LaC3N3O3 also shows a slightly stronger effect on tensile strength of PVC than La(St)(3). Therefore, the LaC3N3O3 can be used to replace La(St)(3) and serve as a costabilizer to improve stabilization efficiency of calcium/zinc stabilizers for PVC. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers