To replace traditional toxic Sb2O3 flame retardants, Bi2Sn2O7 (BSO) nanoparticles were prepared by a coprecipitationmethod and used as flame retardants of flexible polyvinyl chloride (PVC) for the first time. Structural characterization revealed that as-prepared BSO nanoparticles had a cubic phase with an averagediameter of 20 nm. Under 3 wt% loading, the PVC/BSO composite gained a limiting oxygen index of29%, very close to 29.5% of PVC/Sb2O3. In particular, the PVC/BSO composites passed the UL-94V-0 rating,while PVC/Sb2O3 failed. The PVC/BSO composite also showed better heat and smoke suppression performancethan Sb2O3, with a 27.4% decrease in peak heat release rate and a 39.9% decrease in total smokeproduction, compared with the PVC matrix. The excellent performance is attributed to following two reasons:In the gas phase, similar to Sb, Bi can form BiCl3, which dilutes the combustion gas and captureshydroxyl radicals; In the condensed phase, Sn in BSO helps form more protective char residue with theleast pores and the highest degree graphitization. In addition, the tensile strength and elongation at breakof PVC/BSO were also slightly superior to those of PVC/Sb2O3. In conclusion, BSO nanoparticles will be apromising substitute for toxic Sb2O3 flame retardants.