The present study was conducted with an aim to assess water quality of Tlawng river, a major source of potable water in Aizawl district of Mizoram, for a period of two years, i.e. from February 2007 to January 2009. The data analysed were compared with WHO (2004) and BIS-10500 standards. The average DO content ranged from 5.83 to 6.83 mgL-1 where the lowest DO level shows below permissible limit; BOD from 0.48 to 0.84 mgL-1 which indicates a low organic content in the water; total hardness from 48.75 to 102.71 mgL-1 CaCO3; calcium hardness from 29.14 to 56.14 mgL-1 CaCO3; magnesium hardness from 19.66 to 46.57 mgL-1 CaCO3 and fluoride content from 0.38 to 1.08 mgL-1 where some of the water samples shows below permissible limit. The DO content was negatively correlated with other parameters studied.