BACKGROUND:: Composite resin is a common material used for clinical oral filling and bonding, in which a large number of inorganic fillers play an important role in the mechanical and biological properties of composite resin. It has not been reported that strontium-substituted hydroxyapatite nanoparticles are used as composite resin additives. OBJECTIVE:: To observe the effects of strontium content and dispersant on preparation of strontium-substituted hydroxyapatite nanoparticles and the effects of strontium-substituted hydroxyapatite nanoparticles on the mechanical properties of dental composite resin. METHODS:: Strontium-substituted hydroxyapatite nanoparticles were prepared from strontium chloride, calcium nitrate, ammonium dihydrogen phosphate as raw materials by hydrothermal method. Its structure and surface characteristics were observed by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and the effects of silylation strontium-substituted hydroxyapatite nanoparticles on flexural strength and compressive strength of composite resin were observed. RESULTS AND CONCLUSION:: Low-crystalline needle-like strontium-substituted hydroxyapatite nanoparticles were successfully prepared. Composite resin had the best mechanical properties with 60% strontium-substituted hydroxyapatite nanoparticles, with its flexural strength of (92.459±3.285) MPa and compressive strength of (150.573±4.706) MPa. It is indicated that strontium-substituted hydroxyapatite nanoparticles can improve the mechanical properties of dental composite resin.Guo YJ, Cheng H, Zhang SP, Li XR.Preparation of strontium-substituted hydroxyapatite nanoparticle and its influence on mechanical properties of dental resin. Zhongguo Zuzhi Gongcheng Yanjiu yu Linchuang Kangfu. 2010;14(38): 7124-7128. [http://http://www.crter.cn http://en.zglckf.com]