The flame retardant and smoke suppressant properties of semirigid PVC treated with calcium carbonate (CaCO3), tin oxide (SnO2), the mixture of CaCO3/SnO2 and SnO2-coated CaCO3 have been studied through the limiting oxygen index, char yield, and smoke density rating (SDR) methods. The thermal degradation in air of the treated semirigid PVC was studied by thermogravimetry (TG) and differential thermal analysis (DTA) from ambient temperature to 1073 K. The morphologies of the additives and the char formation were studied through SEM. The mechanical property was also studied. The results showed that the semirigid PVC treated with SnO2-coated CaCO3 has a higher limiting oxygen index and char yield, lower SDR and MSDR, a more compact structure of char formation than the semirigid PVC without flame retardant and the semirigid PVC with the equivalent CaCO3, or SnO2, or the mixture of CaCO3/SnO2, a similar tensile property and greatly improved impact strength compared with that of the semirigid PVC without flame retardant. (c) 2006 Wiley Periodicals, Inc.