In Cambodia, agriculture is the important industry which engages many people. However, the water supplied only during rainy season is the source of water for agriculture. To use the limited water resources effectively, it is necessary to apply the water-resource management based on the meteorological prediction and the river runoff prediction. As the factor of these predictions, the soil moisture plays a key role in water and thermal transportation to the atmosphere, and the contribution of river runoff property. On the other hand, the soil moisture distribution with the paddy field scale is helpful in the agricultural activity and management. Therefore, Synthetic Aperture Radars (SAR) is expected to observe soil moisture with high spatial resolution in large area. Recently, some multi-polarization SAR have been in operation. The purpose of this study is to develop the algorithm to estimate soil moisture by using multi-polarization data acquired with the Phased Array type L-band Synthetic Aperture Radar (PALSAR) onboard the Advanced Land Observing Satellite (ALOS).