Inverse Synthetic Aperture Radar (ISAR) Imaging with Low Signal to Noise Ratio (SNR) is one of difficulties in radar target detection. A new technique for ISAR motion compensation with low SNR is presented. For the range alignment, the cross-correlation method based on the exponential weight accumulative gliding window is applied to achieve the coarse range alignment. The precise range alignment within a range cell is accomplished by introducing minimum entropy method. In auto-focusing, the coarse focusing is achieved by the cross-correlation method and minimum entropy criterion is utilized to precisely focus the ISAR image. Experimental results with measured data of aircraft illuminate the robustness of the minimum entropy motion compensation technique.