Recently, much attention has been focused on the miniaturized fiber interferometer devices due to their advantages of compact structure, small size and low cost. In this paper, we introduce two types of miniaturized fiber Mach-Zehnder interferometer (FMZI) and fiber Fabry- Perot interferometer (FFPI) and their applications as fiber sensors. An in line miniaturized FMZI could be fabricated by discharge or a point hydrogen flame. Here, we demonstrate its application as a fiber temperature sensor. A miniaturized FFPI could be fabricated by discharge when a hollow core photonic crystal fiber is spliced to a single mode fiber. Here, we demonstrate its application as a liquid refractive index sensor.