Abstract X-ray diffraction measurements of the liquid TlTlAsSe 2 system were carried out over the composition range from 0 to 80 mol%Tl. The electrical conductivity, magnetic susceptibility and thermoelectric power of this system were also measured over a wide temperature range. The first peak at 2.3 Å in the distribution function, G(r), observed in the low Tl concentration range below 40 mol%-Tl was assigned to the nearest neighbour AsSe interaction and the coordination number n AsSe=3 was obtained. This implies the AsSe chain structure in the solid state remains undestroyed on melting in this composition range. In the Tl rich region above 60 mol%Tl, the nearest neighbour AsSe peak becomes unclear and G(r) at 80 mol%Tl seems rather similar to that of pure Tl. The diffraction results and electronic properties observed suggest that the nearest neighbour TlTl interaction acts an important role in the Tl rich region.