The present study investigates total phenolics, flavonoids, and in vitro antioxidant activities in methanol extracts of roots, stems, leaves, and fruits of medicinal herbs (Phyllanthus fraternus G.L. Webster; Bhui-amla and Solanum nigrum L.; Makoi or black nightshade) of Indo-Gangetic plains of India. The results showed that biochemical attributes of methanol extracts of both the tested plants varied significantly with sites (P < 0.05). Contents of total phenolics and flavonoids and antioxidant properties were found highest in fruits followed by leaf, stem, and least in root of P. fraternus and leaves, fruits, stem, and roots of S. nigrum plants. The present investigation revealed that total phenolic content in fruits of P. fraternus ranged from 26.69 to 61.48 mg GAE/g fw and from 8.89 to 24.69 mg GAE/g fw in leaves of S. nigrum plants, and thus, these plant parts can be promoted for pharmaceutical purposes and health benefits. It is also suggested that the individual phenolic compound in the different parts of tested plants should be analyzed to identify their elite population for their mass cultivation, conservation, and sustainable utilization.