Abstract: To understand environmental conditions in River Ase Niger Delta, Nigeria, a study was carried out to assess the faunistic composition of macroinvertebrates as well as the water quality status of the river between the months March and August 2006. Two sampling sites each 25 m long were selected along a 20 km stretch of the stream. Water temperature, flow velocity, dissolved oxygen, pH, conductivity, total alkalinity and phosphates were similar in both stations sampled. BOD(5), water depth and nitrates were significantly higher in station I and showed wide temporal variation. Pearson correlation coefficient analysis indicated temporal trends in macroinvertebrate density and community composition. This was related to changes in environmental characteristics of the river especially BOD5 and amount of nutrients. These factors produced spatial and temporal heterogeneity and exerted major influence on the macroinvertebrate communities. Thirty-six morphologically distinct taxa representing eleven orders were recorded. The most abundant group was Coleoptera, which made up 38.5% of the total number of macroinvertebrates collected followed by Diptera which accounted for 29.3% of the total. Dugesia (Planaria), Agraylea (Trichoptera) and aquatic mites (Hydracarina) were only sporadically present. Analysis of faunal similarity using Jaccard`s similarity index showed that the fauna of both stations were dissimilar with station II recording comparatively high abundance and diversity of macroinvertebrates. The differences observed could be attributed to the nature of the habitat, general water conditions and substratum at the sites sampled.