Abstract: The nano-sized SiO2 was grafted and modified with 3-mercaptopropyl trimethoxysilane（KH590）.The influences of KH590 content，reaction time，and temperature on grafting rate and particle size of nano-sized SiO2 were studied.The modified and unmodified SiO2 were characterized by Fourier transform infrared spectroscopy（FT-IR） and scanning electron microscope （SEM）.Results showed that KH590 was successfully grafted on the surface of nano-sized SiO2 through the reaction with the hydroxyl groups on the surface of SiO2 after hydrolysis；the optimal modification conditions were as follows：KH590 content was 15%（mass fraction） based on SiO2，reaction temperature was 80 ℃，and reaction time was 10 h；The relative grafting rate could reach 10.3%;and compared with the unmodified SiO2  particles，the modified SiO2 particles showed smaller size，better dispersion and lipophilicity.

Key words: nano-sized SiO2, 3-mercaptopropyl trimethoxysilane, surface grafting modification