Plants, miracle of nature, are able to synthesize hundreds of chemical compounds for various metabolic functions. Numerous phytochemicals (secondary metabolites) with potential biological activity have been identified in most of the plant species. In order to determine the proximate composition, phytochemical analysis and antioxidant capacity of three well known selected plants species, a study was carried out during June 2016 in Khyber Pakhtunkhwa Peshawar. The plants under study were Aloe vera Linn (leaves), Cannabis sativa Linn (whole plant) and Mentha longifolia Linn (whole plant) in PCSIR Labs Complex Peshawar. The results from proximate analysis indicated that the plants contained crude protein in the range 0.447 to 0.953%, crude fiber ranged from 12.33 to 28.47 % and crude fat in the range of 5.87 to 14.86%. Furthermore, analysis showed the presences of important phytochemicals such as tannins, flavonoids, alkaloids, glycosides and saponins in the investigated species. Antioxidant activity of the selected plants by DPPH (2,2-diphenyl-1-picrylhydrazyl radical) scavenging assay and using ascorbic acid as a standard indicated that Cannabis sativa and Aloe vera has the strongest and nearly the same activity with IC50353µg/ml. These plants can be used as herbal products.