A CW Nd:YAG master oscillator - fiber power amplifier (MOPFA) with fiber based SBS phase conjugate mirror is reported. A two-pass amplifier configuration is employed to compensate beam distortions in the multi-mode diode pumped Yb-doped fiber amplifier in conjunction with a fiber phase conjugator. The compensation of distortions is observed with ~30% of the total reflected power being of diffraction limited quality. Possibilities for improving the beam quality and power scaling in this system is proposed.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.