Optical fiber amplifiers offeres basically polarization-indenpendent gain. However, they have polarization fluctuation and polarization mode dispersion (PMD) due to birefringnence in fibers, and still have small polarization-dependent properties such as polarization hole burning (PHB) and polarization dependent loss (PDL). In this paper, these properties are reviewed. Compensation of these properties are also reviewed, with emphasis on the reflective fiber amplifier using Faraday rotator mirror (FRM).