Composite solid state lithium ion electrolytes consist of cubic-garnet structured Li7La3Zr2O12 and NASICON structured Li1.3Al0.3Ti1.7(PO4)(3) with different weight ratios have been prepared. XRD, FESEM and EIS were used to characterize the samples. The highest total ionic conductivity as much as 1.84x10(-6) S/cm was obtained when the weight ratio between LLZO and LATP equals 7:3.