An high-quality open-access database of density and viscosity measurements for the positive and negative electrolytes of vanadium redox flow batteries has been presented. The data contains 272 measuring points across a wide parameter space, including state of charge, total vanadium concentration, sulfate concentration, and temperature. The experimental data has been used to derive empirical regressions that provide the density of both electrolytes with a RMSE below 10 -3 g/cm 3 , and the viscosity with a RMSE of 1.48 • 10 -2 mm 2 /s for the posolyte and 3.16 • 10 -2 mm 2 /s for the negolyte.