In the case of Iran with arid and semiarid climate and lack of freshwater, pay attention to water quality and its effective factors is necessary. Karkheh watershed is more than 5 million hectares in area and with biggest soil dam in Asia, which has widespread land use changes in last decades. The most important factors of water volume and water resources reduction are aridity and improper land use. In this research at first survey of land use changes on the 5 sub-basins of the watershed over a period from 1988 to 2002 accomplished, using TM and ETM land set satellites. Then water quality changes have been studied in this period. Results show that land use changes are tending to reduction of ranges, forests, gardens and agriculture lands, and the increase in sterile lands. The area of urbane lands on the entire of watershed increased from 19051 to 27794 hectares in the period of 1988 to 2002. Studding the land use changes in different sub-basins separately shows the increase in urbane lands in the most of which. The increase in agriculture and garden lands was also seen in two sub-basins, Kashkan and South-Karkheh. On the other hand the water quality of Karkheh River shows severe loss, as increased by the parameter EC, TDS, SAR and Anion and Cation in the course of study shows. Therefore, the results indicate water quality reducing as a result of land use changing. As well, the available data in this region show drought over period of 1998-2000, that with land use changes cause reduction of discharge and therefore reduction of water quality.