The density of molten Ni-Ta alloys has been measured by a modified pycnometric method. It is found that the density of the molten Ni-Ta alloys decreases with a rise in temperature, but increases with the increase of tantalum concentration in the alloys. The molar volume of molten Ni-Ta binary alloys increases with the increase of temperature and tantalum concentration. The partial molar volume of tantalum in molten Ni-Ta binary alloy has been approximately calculated.