A study on the Water Quality Index (WQI) has been conducted among 11 rivers in Penang Island, Malaysia from October 2012 to January 2013. The water quality status of rivers was classified based on the Interim National Water Quality Standard (INWQS) for Malaysia. The six water quality parameters used to determine the water quality index are dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solid (TSS), ammonia and pH value. Based on the WQI assessment, among the 11 rivers studied, none of the rivers were considered as clean. The upstream and middle stream of the Pinang River in Balik Pulau (with WQI = 69 and 70 respectively), the upstream and middle stream of the Kongsi River (with WQI = 67 and 72 respectively) and the upstream of the Betong River (with WQI = 63) were slightly polluted, while the rest of the rivers had a WQI of below 60, which were categorized as polluted rivers. Among the 30 sampling stations, 17 stations were classified as Class III (extensive treatment of water supply required; fish for common economic value, species tolerance, and for livestock drinking), and 13 stations were classified as Class IV water status, which was classified as irrigation according to INWQS. From this study, the WQI and river classification system were considered as a tool for assessing the health status of river water quality. Efficient and sustainable management of rivers in Penang Island should be emphasized in order to protect their aesthetic value for future generations.