This study examined the presence and sources of 10 pharmaceuticals in Klang River were studied. The most common pharmaceuticals were caffeine and acetaminophen, 0.57-20.62 ng/mL and “not detected”-1.45 ng/mL. Water samples were clustered based on pharmaceutical concentrations. Source apportionment analysis showed that treated wastewater discharged from treatment plants contributed 18.43% of pharmaceuticals in Klang River. An environmental risk assessment by means of the risk quotient (RQ) was done whereby the latter was more than one for salicylic acid and diclofenac in surface water posing threats to the aquatic environment. Salicylic acid showed high risk for acute toxicity, while diclofenac showed high risk for chronic toxicity. The results indicated a need for regular monitoring on pharmaceutical levels in Klang River and increasing the efficiency of wastewater treatment here.