In recent years, polarization-maintaining (PM) microfibers have attracted much research attention mostly due to their ultra-high birefringence and large evanescent field effect. This article starts from introduction of the structures, fabrication methods, and mode characteristics of PM microfibers. Different previously-implemented PM microfiber sensors have been presented. The two polarization modes may have different responses on changes of external parameters for PM microfiber, which allows fabrication of polarization-related devices, such as interferometers or gratings. Some sensing characteristics, such as extremely-high refractive index sensitivity and/or temperature-independent response, have been demonstrated. The sensing applications including detection of refractive index, humidity, magnetic field and specific DNA molecular have been described in detail. This article should be helpful for future development of PM micro/nano fibers and the related sensors.