During extensive and intensive exploration of naturalized aliens or exotics from Vidarbha region of Maharashtra state, in last ten years 2003 - 2014, in all 233 plant species were collected from various localities of Vidarbha. These species are naturalized in forest vegetation, along road sides, on margin of ponds, rivers, dams constructed by government. Simultaneously every year, effect of these plants on natural vegetation was studied with continuous observation. Some are maintaining phyto-sociological relationship at the same time, most of the naturalized aliens are producing large number of communities and replacing native species, also they are harmful to human health and animals, some are allergic causing number of skin diseases, dysentery, diarrhoea, gastro-intestinal tract diseases, blindness, bronchial asthma, cough, etc.