Hydrothermal disposal of sodium arsenate waste was investigated with the aim of removing As from solution, and its precipitation as crystalline iron arsenate. The precipitate was characterized by XRD and SEM, and leach tests were conducted to examine the precipitates solubility. The optimum formation condition for crystalline iron arsenate was pH 0.3-1.7, temperature 150-200 degrees C, Fe/As 1.0 and time 10-40 min. Over 98% arsenic in the waste can be precipitated. The solid product is mainly iron arsenate which has a solubility below 5 mg/l. The preliminary work showed that hydrothermal disposal is a feasible option for treatment of sodium arsenate waste.