Spherical cobalt hydroxystannate was prepared and characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analyzer–Fourier-transform infrared spectroscopy. Results showed that cobalt hydroxystannate spheres have an average particle size of 440 nm and disperse uniformly. The flame-retardant flexible poly(vinyl chloride) treated with cobalt hydroxystannate was studied by the limiting oxygen index, universal tensile testing machine, thermogravimetric analyzer–Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and laser Raman spectra methods. Compared with the pure poly(vinyl chloride), the limiting oxygen index value of the poly(vinyl chloride) sample (PVC/10) treated with 10 phr of cobalt hydroxystannate is increased by 4% points, and its total heat release and total smoke production decreased by 18% and 50%, respectively. The result could be attributed to the water produced by the dehydration of cobalt hydroxystannate, and the interaction of cobalt hydroxystannate and the poly(vinyl chloride) matrix, which produces dense and highly graphitized char residue containing hexagonal phase graphite, CoCl2, Co2O3, and Co3O4.
