The dynamic and equilibrium surface tension (ST) data of proteins such as bovine serum albumin (BSA) are crucial in numerous theoretical and practical applications. However, reliable equilibrium ST of BSA is absent in the literature. This study illustrates a more precise and accurate approach for measuring equilibrium ST of aqueous BSA solutions. The ST relaxation of aqueous BSA solution [C = 0.052–15 (10^-10 mol/cm³)] was monitored using a pendant bubble tensiometer for 2–5 days, depending on the BSA concentration. The dynamic ST indicated that irrespective of the BSA concentration, the ST remained nearly constant at the latter stage for several tens of hours. These ST values were further confirmed by a perturbation process (a forced, rapid expansion/compression of the bubble surface). The data indicated that the equilibrium ST of BSA_(aq) solutions remained essentially unchanged over a wide range of BSA concentration [C = 0.052 to 15 (10^-10 mol/cm³)] at 51.5 ± 0.3 mN/m.