The density of Ni-Co-Al ternary alloys with a relative fixed mole ratio of Ni/Co(xNi:xCo≈86:14) and aluminum concentration change from 0 to 10% mass fraction in liquid states were measured by a modified pycnometric method(MPM). It was found that the density of the liquid Ni-Co-Al alloy decreases with increasing temperature, Al concentration and the ratio of Al concentration to Ni concentration in the alloy. The temperature coefficient of density changes with increasing the Al concentration or the ratio of Al concentration to Ni concentration in the ternary alloys. The measured densities by MPM were comparable with that by the modified sessile drop method, the maximum difference of density between them was about ±0.56%. The molar volume of liquid Ni-Co-Al alloy increases with increasing temperature and changed with increasing Al concentration. And the partial molar volume of aluminum in Ni-Co-Al alloy was calculated approximately. The molar volume of liquid Ni-Co-Al ternary alloy determined in the present work shows a negative deviation from the ideal linear molar volume.