The electrical conductivity of the molten Lil-TlI system has been measured as a function of composition and temperature. The observed electrical conductivity shows a large negative deviation from the additive law. The observed chemical shifts of205T1 NMR in the molten Lil-TlI system increase linearly in the diamagnetic direction (high field) with increasing Lil concentration. The chemical shifts for each composition increase in the paramagnetic direction (low field) with increasing temperature. These behaviors are interpreted from the change of overlap of the Tl-I orbitals. The observed very fast spin-lattice relaxation rates of205Tl are attributed to the formation of paramagnetic centers such as Tl2+in the melts.