Lithium-ion Conductive Solid Electrolytes have attracted the particular interest for possible applications as solid electrolyte of lithium ion secondary batteries and many studies for them have been carried out. In recent years, the crystal structures, the ionic conductivity and the dynamics of component ions for a series of compounds MBr-m' Br3 (M=Li, Cu, Ag ; M'=Al, Ga, In) was investigated and it was found that Li3InBr6 is a good lithium ion conductor with high ionic conductivity, α～10-3 Scm-1, at 330 K. Because this solid electrolyte, Li3InBr6 shows such high conductivity only at high temperature phase, I tried to dope this compound with another element to improve its ionic conductivity in this study. In Li3InBr6 doped with divalent cations (M=Mg, Ca, and Ba), the conductivity decreased with x unfortunately, accompanied by a broadening of the 115In NMR spectra. In Li3-2xSrxInBr6(x ≤ 0.7), the conductivity of high temperature phase also decreased with an increase of x but LiSrInBr6 show almost the same conductivity to Li3InBr6. The conductivity of the low temperature phase in Li3-2xMgxInBr6(x ≤ 0.4) increased with x. On the other hand, in the case of the compounds doped with CI ion, Li3InBr6-xClx, phase transition temperature lowered in the compound of x = 3 and the high ionic conduction phase is stable under the room temperature. Furthermore, the value of the ionic conductivity of the Li3InBr3Cl3 was almost equal to the original Li3InBr6.