We have analyzed most of the commonly used burst-mode focusing algorithms and chose the one that can be easily combined with unsynchronized-signal removal. In order to remove the unsynchronized signal in scanning synthetic aperture radar (ScanSAR) interferometry, we calculate the burst synchronization using satellite state vectors at first. Then, based on the focusing algorithm chosen and the synchronization calculated, we propose a method to remove the unsynchronized signal. The method rejects the unsynchronized phase and keeps all of the magnitude information. It has been tested with simulated Envisat Advanced Synthetic Aperture Radar ScanSAR data, and the result demonstrated that the method could effectively remove the unsynchronized signal for ScanSAR interferometric processing.