Abstract: By comparison with tribasic lead sulfate (TLS) and N,N-dimethyl-6-aminouracil (DMAU), the thermal stabilization of N,N-dimethylcyanoacetylurea (DMCAU) in poly(vinyl chloride)(PVC) was studied by Congo red and oven aging method. It showed that the thermal stability of DMCAU based system was similar to that based on DMAU. When DMCAU was used alone and the dosage was low, the Congo red test time was longer than that of TLS. With increasing dosage, the increase in test time was far slower than TLS, and the inhibiting effect for PVC′s discoloration in oven was no better than TLS. When DMCAU was used with CaSt, a synergistic effect was observed in Congo red test, and the optimal proportion was 1∶1.