In order to further improve the refractive index sensitivity of long p eriod fiber grating (LPFG),a LPFG-based sensor modified with nano titanium dio x ide (TiO₂) particles is fabricated.The response of sensor to external refracti ve index and temperature change are investigated experimentally.The hydroxyl gro up produced by hydrolysis of TiO_2surface was combined with carboxyl group on po lyacrylic acid to achieve the modification of TiO₂.The LPFG-based sensor modi fi ed with nano TiO_2particles on the fiber surface is formed by covalent bonding . The response characteristics of the sensor to refractive index and temperature a re studied experimentally.The results show that the resonant wavelength of TiO 2-LPFG move to shorter wavelength with the increase of refractive index.The ave r age refractive index sensitivity of TiO₂-LPFG is 45nm/RIU in the refractive ind ex range of 1.3331－1.4485,which is 1.2ti mes higher than that of bare grating; and the temperature sensitivity of the sensor is －0.0503nm/ ℃,which is far low er than the refractive index sensitivity.The proposed sensor has an advantage o f low cost and easy to manufacture.Additionally,the enriched oxygen-containin g functional groups are fixed on the surface of the sensor,making it has a wide application in the fields of biological and medical.