The study was carried out on Mustard (Brassica juncea, L.) to (i) determine the proximate composition of the seeds, leaves, shoots and roots; and (ii) determine the concentration of bioactive secondary metabolites on the seeds, leaves, shoots and roots. The experiment was conducted at the Central Laboratory, National Root Crop Research Institute (NRCRI), Umudike, Nigeria. Cultivated mustard seedlings were sourced from existing experimental plot at Teaching and Research Farm, Federal College of Agriculture, Ishiagu, Nigeria. Various components of mustard seedlings were extracted using water. The samples were screen to determine active secondary metabolites, proximate composition and nutritional compounds. The results revealed a significant difference in the proximate content in the seeds, leaves, stem and root of the plant. The roots had the highest moisture content (13.62) while the stem had the least (6.38). Stem had the highest dry matter content (93.64) while the roots had the least (86.36). Roots had the highest crude fiber content (20.06) while seeds had the least (7.05). The crude protein content varies with different plant parts such as roots, stems, leaves and seeds with values of 6.71, 7.10, 12.55 and 18.13 respectively. There is a significant difference in phytochemical compounds present in different parts of the plant. The current study domstrates that mustard plant's potential as a food source and raw material in both human and plant medicine.

Keywords: Brassica juncea, secondary metabolites, proximate composition and nutritional compounds.