We use corrosion inhibitors, for the first time, to protect GMR biosensor from corrosion in phosphate buffer saline (PBS) solution. A very uniform thin protective film (5-10nm) is formed on the surface of biosensor (including contacts). To make this protective film more effective, a multi-step process is developed. In the first step, protective film is formed in deionized water containing corrosion inhibitors with minimum initial corrosion and defects. Biosensors are then immersed in PBS solution containing corrosion inhibitors. In this step, any defects due to the attack of chloride ions could be self-repaired in the presence of corrosion inhibitors. Finally, biosensors with protective film are ready to test in PBS solution without any corrosion inhibitors. The exciting results show that as-prepared protective film is stable in PBS solution without any inhibitors for up to 15 days.