A Li1.4Al0.4Ge1.6(PO4)3 (LAGP) sheet was prepared using a tape casting method with a fine LAGP power prepared from a sol–gel precursor. The addition of nanosize TiO2 as a sintering additive was effective to enhance the ionic conductivity of the tape-cast sheet. The highest electrical conductivity of 8.37 × 10−4 S cm−1 was observed for the tape-cast LAGP sheet with 5 wt.% TiO2 at 25 °C. A hybrid sheet of the tape-cast LAGP and epoxy resin was water impermeable. The electrical conductivity of the water impermeable hybrid sheet with ca. 4% epoxy resin was 4.19 × 10−4 S cm−1 at 25 °C. The three-point bending strength of the LAGP–5 wt.% TiO2–epoxy resin hybrid sheet was 111 N mm−2, which is comparable with a Li1+x+y Al x Ti2−x P3−y Si y O glass ceramic plate. The Li/PEO18(CF3SO2)2N/LAGP–5 wt.% TiO2–epoxy sheet was successfully operated as a lithium electrode in saturated LiCl aqueous solution.