A one-step hydrothermal method is employed to produce protective magnesium hydroxide films on ZK60 magnesium alloy samples. Samples with morphologies resembling small flakes, strips, and hexagonal flakes are produced depending on the preparation temperature and time. A higher temperature accelerates nucleation and growth of Mg(OH)2 and the morphology of Mg(OH)2 depends on the treatment time. The sample prepared at 120°C for 24h is covered by a 1.78μm thick magnesium hydroxide film with the preferred (101) orientation and exhibits the best corrosion resistance. The results disclose a simple and environmental friendly method to protect the magnesium alloy by forming a self-sacrificing layer of Mg(OH)2.