The electrical conductivity, magnetic susceptibility, and thermoelectric power in the liquid (Tl1/2Pb1/2)-Se system are measured over wide temperature and composition ranges. It is observed that the electrical conductivity in the system sharply falls near the stoichiometric composition of Tl2Pb2Se3 and the magnetic susceptibility has a diamagnetic maximum at this composition, where the thermoelectric power changes its sign. In addition, the DTA investigation shows that the liquidus temperature of the system has a maximum around this composition. These results suggest that a short-range order appears around the composition of Tl2Pb2Se3 in the liquid (Tl1/2Pb1/2)-Se system. The delocalized electron analysis using both susceptibility and conductivity data suggests that the bonding nature of liquid Tl2Pb2Se3 is rather ionic. The radial distribution study by neutron diffraction also exhibits that the first peak position of g(r) for liquid Tl2Pb2Se3 is located near the ionic bond distance of metal and chalcogen atoms. On the other hand, covalent Se-Se bonds are formed in the Se-rich composition range.