Rates of reaction of nitrogen with thorium were determined for the temperature range of 670° to 1490°C at 1 atm pressure. The reaction follows a parabolic law and the parabolic rate constant in (ml/cm2)2/sec is . The activation energy of reaction has a probable error of 1300 cal/mole. Rates of diffusion of nitrogen in thorium were obtained over the temperature range of 845° to 1490°C at atmospheric pressure. The diffusion coefficient in cm2/sec is . The activation energy of diffusion has a probable error of 1300 cal/mole. Limiting solubilities of nitrogen were determined from the diffusion data. The heat of solution of atomic nitrogen (from ) in thorium is .