The microfiber-optic interferential sensor based on polyaniline (PANI) sensing layer is efficiently performed in pH detection. The refractive index changes of PANI film can be translated into a significant wavelength shift in the interferometric fringe. We demonstrate the feasibility of PANI attached to the fiber surface in studying the interface polymerization method. The sensing performances of an improved sensitivity in acid solution with -0.54nm/pH and alkaline solution with 0.28 nm/pH are systematically investigated. By taking advantage of its miniature size and mechanical flexibility, the microfiber interferential sensor might make a promising platform for pH measurement.