The aim of this study is to demonstrate different applications of the passive and active sensor data for different forest studies in Mongolia. For this purpose, Landsat TM data of 1988, SPOT XS image of 1997, ERS-1/2 tandem pass SAR images of 1997, ERS-2 SAR and JERS-1 SAR intensity images of 1997, and other thematic information are used and different digital image processing techniques are applied. The results indicated that the integrated use of optical and microwave data can be successfully used for different forest studies as well as for differentiation between the fuzzy boundaries of different forest and vegetation classes.