Since 2003, the benthic macro-invertebrate has been considered as one of the four im groups of aquatic organisms for assessment of the ecological health in lower Mekong river including Thailand, Laos PDR, Cambodia anc! Vietnam. In 2009, the authors applied the standard methodsd Mekong River Commission in "Ecological Health Monitoring (EHM)" to sample and analyse the macroinvertebrates at seven sites of Sai Gon river, in Binh Duong province, in both dry and seasons. A total of 32 species, in 6 classes, 3 phyla of macro-invertebrates were recorded in the area. Among them, river mussels, insect larvae, polychaete worms and oligochaeta worms are the diverse groups in terms of species composition. These groups are also widespread and dominant in study area. Biological water quality of bottom layer in the dry season is lower than in the rainy 5 and gradually decreased in downstream. The biological water quality is the lowest at the site of Binh Duong bridge.