A novel fiber optic resonator employing a 90 degree polarization rotation was developed to reduce polarization related bias errors of the resonator fiber optic gyro. For the first time, we have fabricated and tested a nearly all guided-wave gyro having a polarization-rotating fiber resonator. Bias stability better than 0.4 deg/hr, random walk of 0.1 deg/root-hr, and day to day absolute bias stability of 10 deg/hr are reported. The major error mechanism of bias instability and other error sources are discussed.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.