This study is highlighted to investigate the characteristics of pollutant runoff and relationships between pollutant load and runoff in an urban area of Vientiane city, Lao PDR. Hong Thong catchment area was selected for sampling during wet and dry weather. As a result of the survey, mean concentration of SS was higher in rainy season, in contrast, COD, TN and TP were much higher in dry season possibly due to being associated with domestic wastewater, and attenuation by stormwater in rainy season. The mean total PAHs concentration value were 230.13, 132.83 and 143.72ng/L respectively for rainy season wet and dry periods, and dry season. Base on the composition of specific components, PAHs in Hong Thong catchment area was determined to be derived mainly from oil discharge rather than fuel combustion.