Organic-inorganic hybrid solid electrolytes composed of Li+-conducting lithium aluminum germanium phosphate (LAGP), poly(ethylene oxide) (PEO), lithium perchlorate and succinonitrile (SN) were prepared in the form of flexible thin film, and their electrochemical properties were investigated. The hybrid solid electrolytes showed high ionic conductivities ranging from 3.0×10−5 to 1.1×10−4 Scm−1 at room temperature and exhibited good electrochemical stability. A solid-state Li/LiFePO4 cell assembled with hybrid solid electrolyte composed of 70wt.% LAGP, 21wt.% PEO-LiClO4 and 9wt.% SN delivered a high discharge capacity and exhibited good capacity retention at ambient temperature. Good cycling performance of the cell resulted from the high ionic conductivity of the solid electrolyte and its good interfacial contacts with electrodes.