The solubility of Th(NO3)4 in water is a linear function of temperature in the range 5-60°C. The density was measured at concentrations up to saturation, at 25-60°C, and the conductivity and pH of Th(NO3)4 solutions were determined at the same temperatures. The equivalent conductivity at infinite dilution was 72, 89, 104, 123 Ω-1 cm2 equiv.-1, at 25, 35, 45, 60°C, respectively, after correction for a hydrolysis reaction. The viscosity increases greatly at about 1 mol l.-1 concentration. Depression of freezing points was determined, the lowest point attained being -37°C, which corresponds to a 2.9 mol kg-1 solution.