The ionic conduction in the systems of Li4SiO4-Li3VO4 and Li4GeO4-Li4SiO4-Li3VO4 has been studied in the temperature range from room temperature to 300℃. It is found that the γII-phase solid solution Li3+xV1-xSixO4, are good ionic conductors. Among the compositions studied Li3.3V0.7Si0.3O4 is the highest ionic conductivity which reaches 1×10-5Ω-1·cm-1 at room temperature with activation energy 0.36eV in the temperature range 42°-192℃. It's electronic conductivity is negligible, therefore it is one of the best lithium ionic conductors discovered so far. The high conductivity domains in system Li4GeO4-Li4SiO4-Li3VO4 have been roughly determined. It is found that the substitution Si for Ge in Li3.5V0.5Ge0.5O4 can cause the ionic conductivity increase. The ionic conductivity of Li3.5V0.5Ge0.4Si0.1O4 at room temperature is 1.3×10-5Ω-1·cm-1 with an activation energy 0.4eV.