Water samples were collected from Jalsansthan Benajhawar Kanpur sampling station on the Ganga River with in Kanpur city in the year 2008(April) -2009(March) and analyzed for 14 water quality variables (physico- chemical) parameters, The data obtained were standardized and subjected to principal components analysis (PCA) to define the parameters responsible for the main variability in water quality variance for Ganga River with in Kanpur city. The PCA produced two significant main components and explain more than 99.316% of the variance Namely, anthropogenic effect and industrial effect; that represent 64.470% and 34.846% respectively of the total variance of water quality in Ganga River. Results reveal that Total dissolved Solids,Total Alkalinity,Total Hardness were the parameters that are most important in assessing variations of water quality in October, November, December, January, February, March, April(post monsoon season) in the river. Results also reveal Turbidity, Suspended Solid were the parameters that are most important in assessing variations of water quality in June, July , August and September in the river(monsoon season). This study suggests that PCA technique is useful tool for identification of important river water quality monitoring months and parameters. Ca+2, Cl-,SO4 -2,Temperature, Flouride, pH, Fe, Oxygen Consumption(O.C), Cl- , Mg+2 are found to be non principal water quality parameters.