Estuaries are coastal ecosystems which are commonly known to support unique flora and fauna. The Adyar estuary is a severely damaged ecosystem due to developmental activities in the urban city of Chennai, Tamil Nadu, India. Botanical explorations were conducted in and around Adyar estuary during 2008 to 2010 to document the diversity and distribution of angiosperms. A total of 252 species and 2 varieties of angiosperms belonging to 196 genera, distributed in 64 families from 27 orders and 10 clades/groups were recorded and are arranged according to Angiosperm Phylogeny Group III Classification. It is observed that the flora of Adyar estuary also harbours a high level of non-native species. Anthropogenic threats to the estuary and its flora are identified and conservation strategies are briefly discussed.