Accurate data on the high‐temperature thermophysical properties, which are density, surface tension, and viscosity, are indispensable for performing high‐precision casting simulations of Ni‐based superalloys. Viscosity is the most important thermophysical property for thermofluidic analysis. However, measuring the viscosity of an alloy, which is lower than that of molten glass, is difficult, and experimental viscosity data are limited. Herein, the density of Ni‐based superalloys is measured using the maximum bubble pressure (MBP) method to determine viscosity. The viscosity is evaluated using the oscillating crucible method. The surface tension is simultaneously measured using the MBP method. In these results, the average density values [kg m−3] of Alloy 65, Alloy 718, Alloy WA, and Alloy 720 are 7.52 × 103, 7.43 × 103, 7.82 × 103, and 7.52 × 103, respectively. The average surface tension values [N m−1] of Alloy 65, Alloy 718, Alloy WA, and Alloy 720 are 1.55, 1.54, 1.47, and 1.51, respectively. The fitting equations of the molten Ni‐based superalloys are as follows. 1) Alloy 65: ; 2) Alloy WA: ; 3) Alloy 720: ; 4) Alloy 718: .