Purpose: The innumerability of un-researched medicinal plants has occasioned their exceptional and unlimited study. Without a continuous study, the importance and use of many medicinal plants will be spuriously occluded and hence marshal untold limitations to their medicinal value. This research therefore was conducted to unravel the phytochemical constituents and antioxidant activities of Petiveria alliacea L, Hoslundia opposita Vahl, Alternanthera Brasiliana (L.) Kuntze, and Solanum erianthum D. Don. Methods: Standard laboratory procedures were dutifully followed and ensued data were analyzed using SPSS, version 23, 32 and 64 bit. Results: The four analyzed plants were rich sources of major phytochemicals like: tannins, terpenoids, steroids, saponins, phenolics, flavonoids and cardiac glycosides. All the plants also demonstrated high antioxidant activity in DPPH, Fe2+ Chelation, FRAP and Peroxides assays. The best antioxidant activity and IC50 values were obtained from S. erianthum which may be attributed to the highest quantity of phenols and flavonoids it contained in comparison to the rest evaluated plant samples. Conclusion: It was inferred that the observed high antioxidant activity of all the plant samples may be predicable to their plentious quantified phytochemicals. The plants were thenceforth recommended for further study on their acute toxicity (LD50) and with special emphasis on S. erianthum.