The investigation was undertaken with an objective of analyzing the antioxidant capacity of three under exploited leafy vegetables and to study the effect of the hydrothermal processing or domestic way of cooking (boiling)on the bioactive compounds of the underutilized leafy vegetable samples (wild variety) of Celosia argentia, Digera Muricata and Tribulus terrestries extracted using aqueous acetone and methanol and to analyse the difference in biochemical composition when it was subjected to processing was determined by In vitro antioxidant activities. To determine antioxidant activity, we measured total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2,2-azinobis-3ethylbenxothiazoline-6-sulphonicacid (ABTS) cation decolorization activity, Nitric oxide radical scavenging activity, Flavonoids, Metal chelating activity and reducing power. The present investigation evaluated that all processed samples were observed to contain higher amount of phenolics and tannins than their respective raw samples. Significantly higher activity was recorded for aqueous acetone compared to aqueous methanol extracts for all the tested leafy vegetables. The results illustrated that the phytochemical contents of the leafy vegetables serve as supplements for food and also have the potential to improve the health status. Hence there is need to emphasis a diet rich in indigenous green leafy vegetables to promote health and prevent diseases in the population.