Abstract:The present study was carried out to investigate and determine the water quality and the pollution sources affected on Semenyih River using multivariate statistical techniques and water quality index (WQI). Temperature, pH, dissolved oxygen (DO), conductivity, total dissolved solids (TDS), sulfate (SO ), nitrate determined that 96.63% of the total variance was accounted for five factors which pointed to the variables responsible for deterioration of water quality attributed to anthropogenic activities associated with urbanization, industrialization, agriculture, livestock husbandry and mining activities. In addition, WQI classified the river as clean (Class I) at station 1, slightly polluted (Class II) at stations 2 and 3 and as moderately polluted (Class III) at stations 4-8; in general; however, the river falls into class III and thus is required extensive treatment before using for domestic purposes. Therefore, this study verified that the multivariate statistical techniques and water quality index are mainly required for interpreting complex data sets for the purpose of analysis of water quality variations.