This study was carried out to determine the effects of sewage pollution on the fish assemblages found in the Klang River. Samples were collected between July 2012 and April 2013 with a total of 102 specimens belonging to 5 freshwater fish species, Puntius hexazona, Betta livida, Neohomaloptera johorensis, Parosphromenus harveyi and the dominant species, Rasbora sumatrana, with the highest dominance value (Di%=36.66). Multiregression revealed a statistically insignificant relationship among the physical, chemical and biochemical parameters of water and sediment and Puntius hexazona, Betta livida, Neohomaloptera johorensis and Parosphromenus harveyi. Based on multiple regression tests, a significant relationship with R2 = 92.2% and F= 7.876 (p= 0.000) was found between six water and sediment quality constituents and the numbers of Rasbora sumatrana this species at the stations studied at Site 8. On the other hand, water temperature (β= -0.114; t= -2.811 (p= 0.016)); sediment organic matter (β= -0.011; t= -2.406 (p= 0.033)) and water phosphorus (PO4) (β= 0.323; t= 3.444 (p= 0.005)) were found to be the most important water and sediment parameters effecting Rasbora sumatrana.