Solid electrolytes with high ionic conductivity are important for all solid state lithium batteries. NASICON typed LiTi2(PO4)(3) solid electrolytes are synthesized by a simply LiF assisted solid state reaction. The electrolytes prepared with LiF assist exhibit much larger particle size, less voids and higher crystallinity than that of the sample without LiF assist. The LiTi2(PO4)(3) sample synthesized with LiF additive (the molar ratio of LiTi2(PO4)(3):LiF = 1:0.5) delivers lithium ion conductivity of 2.318 x 10(-4) S cm(-1) at room temperature with an activation energy as low as 0.28 eV; while the electrolyte prepared without LiF assist exhibits conductivity of 7.181 x 10(-6) S cm(-1) and activation energy of 0.48 eV. The significantly enlarged conductivity and reduced activation energy suggest LiF assist is an effective and simple method to improve the performance of LiTi2(PO4)(3) solid electrolytes for all solid state lithium batteries.