Li1+xTi2-xSixP3-xO12. Li1+2xTi2AlxP3-xO12, and Li1+xTi2-xAlx(PO4)3(0$leq$x$leq$0.5) were synthesized and the structure the density and the ionic conductivity of samples were investigated. The main structure was a LiTi2(PO4)3 (S.G :R-3CH) phase over all systems except for Li1+xTi2AlxP3-xO12 system in the range of x$geq$0.4 which had LiTiPO5(S.G:Pnma) as a main phase. The density and the conductivity of samples increased with x but de-creased by the precipitation of the second phase. Consequently the ionic conductivity of these system could be enhanced by the increment of the density restraining from precipitating the second phases. The highest. ionic conductivity of 1.29${ imes}$10-3 Scm-1 at 25$^{circ}C$ was obtained in Li1.3Ti2Si0.3P2.7O12