Abstract
In this study, we aimed to grasp the seasonal variation of the water quality in Mak Hiao River which runs in and receives waste water from Vientiane, Lao PDR. The field survey was conducted twice in the rainy and dry season. As a result, total nitrogen, total phosphorus, phosphate phosphorus and toral organic carbon gradually increased flowing downstream in the rainy season and decreased as flow through the suburban area in the dry season.