Electric properties of lithium heptagermanate Li2Ge7O15 single crystal have been studied in AC external field (10(1)-10(5) Hz) in the temperature range 300-700K. It has been shown that below 500K conductivity sigma is determined by polarization processes whereas above this temperature charge transfer phenomena become dominant. It is assumed that at high temperatures conduction is determined by mobile interstitial lithium ions A(Li). The spectra of complex impedance rho* testify for hopping A(Li) conduction and accumulation of charge carriers near to blocking Pt electrodes.