Abstract: The hills of Nallamalais form a part of the Eastern Ghats in Andhra Pradesh, India situated in between 15°20`-16°30` N and 78°30`-80°10` E. The rocks are of Kurnool and Cuddapah formations. The vegetation is broadly divided into forest, grassland and hydrophytic categories. Under climax forest vegetation, three broad types were recognized i.e., southern dry mixed deciduous, south Indian moist deciduous and scrub. Nine edaphic vegetation types were noticed in the study area. Its flora was poorly documented. Therefore floristic surveys were carried out between 1999 to 2006, which resulted in record of total of 1541 angiosperm taxa. They fall under 778 genera and 144 families, bringing out the genus species ratio as 1:2. The dominant families were Poaceae (178 taxa), Papilionaceae (116), Euphorbiaceae (83), Cyperaceae (79) and Asteraceae (63). The life form spectrum was dominated by therophytes (37.1%) denoting a typical tropical arid climate. Nallamalais represents seven worst invasive exotic species namely Cassia uniflora, Lantana camara, Parthenium hysterophorus, Hyptis suaveolens, Mimosa pudica, Cleome viscosa and Prosopis juliflora, which may pose survival threat to the indigenous flora.