Abstract: Cyclomatrix-type polyphosphazene (PZS) microspheres were prepared by one-step precipitation copolymerization of hexachlorocyclotriphosphazene (HCCP) and 4, 4'-sulfonyldiphenol (BPS).Then the microspheres were modified with concentrated sulfuric acid to form sulfonated PZS (SPZS) microspheres.The chemical structure, hydrophilicity and morphology of SPZS microspheres were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, water contact angle test and scanning electron microscopy, respectively.The emulsifying performance of SPZS microspheres was studied using digital photography, optical microscopy and fluorescence microscopy.The configuration of SPZS microspheres on the oil-water interface was investigated by solidifying the oil phase.Results showed that the hydrophilicity of the polyphosphazene microspheres was effectively improved by sulfonation modification.SPZS microspheres could well stabilize a variety of water-oil systems to form fine oil-in-water Pickering emulsions.The packed microspheres at oil-water interface constructed a compact particle film, effectively preventing the emulsion droplets from coalescence.The emulsifying performance of SPZS microspheres was influenced by the microsphere concentration, volume ratio of oil to water and NaCl concentration of aqueous phase.