In this study, the characterisation of the solid waste and the effect of the leachate from the major dumping site in Perungudi, Chennai city, on groundwater is investigated. Various physical and chemical parameters were estimated: this includes pH, total hardness, electrical conductivity, and total dissolved solids, major cations such as Ca2+, Mg2+, NA+ and K+, major anions such as NO3- CI- and SO42- and heavy metals such as Pb, Cu, Mn, Cd, Cr and Zn. Perungudi dumping site receives 1650 tonnes of Municipal Solid Waste (MSW) daily from the Chennai Corporation. The leachate is a result of anaerobic decomposition of MSW. The results of the analysis of the groundwater samples showed that dumping site leachates constitute a serious threat to the local aquifers. Copyright © 2009, Inderscience Publishers.