This research is investigating the performance of JERS-1 SAR and ALOS PALSAR mosaics to map forest cover in Vietnam. Firstly, SAR based forest covers are mapped in 1998 and 2007 respectively using mosaics in 100m grid size supplemented by a validation data provided by Forest Protection Department (FPD) in Vietnam. Secondly three analytical assessments are carried out to evaluate SAR sensors performance for forest cover mapping. It includes (1) effectiveness of polarization with VH and HH, (2) spatial resolution evolution between JERS-1 SAR and ALOS PALSAR and (3) comparison of classification approaches. Finally they are compared with a time series of SPOT VEGETATION and Terra/Aqua MODIS in 1 km grid size over the entire country.