Water quality index (WQI) a tool used to study the quality of water in terms of index number which represents overall quality of water for any intended use. The present study revealed the WQI values of river Ami ranged from a minimum of 91.54 at Rapti river upstream to a maximum of 312.11 at Ami river after confluence of GIDA drain. The higher values of WQI were found mainly due to the higher values of BOD, Nitrate and low value of DO due to addition of untreated/partially treated wastewater emanating from different industries operating in GIDA area in to river Ami. WQI of river Ami is not good even in the upstream (134.5) but it has been improved (121.41) slightly, before meeting to river Rapti. Natural flow of river Ami may be maintained by regulated extraction of water for different purpose and only treated wastewater discharge from GIDA drain.