Methylene blue dyes in is widely used various industries in Indonesia, especially in the textile industry. Methylene blue in waters is toxic and difficult to degrade. One of the methods used is to overcome this problem is photocatalysis under visible light. CuO photocatalyst was prepared using an easy hydrothermal preparation using common autoclave at low temperature. The photocatalytic activity on methylene blue showed degradation up to 63.44%, with optimum pH 9 and the optimum irradiation time of 120 minutes. The photocatalytic activity is influenced by the formation of hydroxyl radicals in CuO, which can degrade dyestuffs. The reaction rate follows second order kinetics.