The flame-retardant and smoke-suppressant properties of soft poly(vinyl chloride) (PVC) treated with zinc hydroxystannate (ZHS), calcium carbonate (CaCO3) magnesium hydroxystannate [MgSn(OH)(6)], strontium hydroxystannate [SrSn(OH)(6)], ZHS-MgSn(OH)(6), ZHS-SrSn (OH)(6), MgSn(OH)(6)-coated CaCO3, SrSn(OH)(6)-coated CaCO3, ZHS-MgSn(OH)(6)-coated CaCO3, and ZHS-SrSn(OH)(6)-coated CaCO3 were studied with the limited oxygen index, char yield, and smoke density rating methods; the mechanical properties were also studied. The results showed that, with the equivalent addition of the corresponding hydroxystannate, the soft PVC treated with hydroxystannate-coated CaCO3 had a higher limited oxygen index than the corresponding hydroxystannate, and the soft PVC treated with the agents containing magnesium had a higher limited oxygen index than the soft PVC treated with the agents containing strontium, except for ZHS-MgSn(OH)(6)-coated CaCO3. The improvement in the char formation of the hydroxystannate-coated CaCO3 was better than that of the corresponding hydroxystannate in most cases, and the aforementioned agents reduced the smoke density rating, decreased the tensile strength, and increased the elongation and impact strength basically. Thermal analysis showed that the additives promoted the evolution of hydrogen chloride, early crosslinking, and rapid charring through the strong catalyzing effect of Lewis acids. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 112:36-43, 2009