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A novel miniature fiber-optic Fabry-Perot (F-P) refractive-index (RI) sensor machined by 157 nm laser is proposed. The sensor head consists of a micro air F-P cavity near the tip of a single-mode fiber with a micro channel on the fiber tip used as both inlet and outlet for medium under test. Thin films are coated at reflective interfaces of the F-P cavity as mirrors to ensure high optical contrast, respectively. A RI resolution of 1130.887 nm/RI unit (RIU) is achieved by experiment. Such a sensor has a number of outstanding advantages when compared with other fiber-optic RI sensors, such as very small, rigid, high resolution, excellent linearity, wide measurement range, et al.