In the present work, Li+ conductor is synthesized via small doping of LiBH4 into "Li-free" compound (or solid solvent), NaI. The formation of solid solution between NaI and LiBH4 is confirmed by XRD measurement, and the solubility limit of LiBH4 exists between 6 to 13 mol%. The value of sigma for 15NaI center dot LiBH4 (6 mol% LiBH4) showed 1.7 x 10(-6) S/cm at room temperature, which is comparable to that for LiI. From the plot of log sigma T vs. 1000/T, an activation energy for Li+ conduction in NaI is estimated to be 0.68 and 0.32 eV for heating and cooling cycle, respectively. The results of AC impedance measurement and DC polarization test indicate that Li+ plays a major role in ionic conduction in NaI regardless of the slight molar fraction of Li+. The present results suggest that the expansion in the material choice for solid solvent and other alkali halides can also work as a base material for Li+ ion conductors.