Envisat Advanced Synthetic Aperture Radar (ASAR) dual-polarization data are shown to be effective for regional forest monitoring. To this scope, an automatic SAR image preprocessing procedure was developed using SRTM DEM and Landsat TM image for geocoding in rugged terrain and smooth terrain areas, respectively. An object-oriented forest and non-forest classification method is then proposed based on the HH to HV intensity ratio and HV images of ASAR data at single acquisition in winter. The developed methods were applied to forest and non-forest mapping in Northeast China. The overall accuracy, the user’s accuracy and the producer’s accuracy of forest are 83.7%, 85.6% and 75.7% respectively. The results indicate that the proposed methods are promising for operational forest mapping at regional scale.