Brassica juncea (Brassicaceae) is used in folklore medicine and in local recipes as source of mustard oil.  In the present study, phytochemical characterization, antioxidant activity, antimicrobial potential and structural elucidation using LC/MS-MS of the crude water and 30% ethanol Brassica juncea extracts were done. 30% ethanol extract exhibited antioxidant activity higher than water extract by using DPPH^• assay with IC₅₀ value of 0.170 and 0.390 mg extract/mL, and by using ABTS^•+ assay with inhibition percent values of 75.5% and 68.9% for 30% ethanol and water extracts, respectively. water extract was slightly higher than ethanol extract in alkaloids and phenolics content while that of ethanol was higher than water in the flavonoids content. The water extract expressed no antimicrobial potential against any of the tested pathogenic strains while that of 30% ethanol expressed broad antimicrobial potential against Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Pseudomonas aeruginosa, Klebsiella pneumonia, Candida albicans, Erwinia Carotovora, Proteus vulgaris Eterobacter cloacae, Shigella sp. and Streptococcus pyogensis. LC/MS-MS profiling of the 30% ethanolic extract showed that caffeic acid, p-coumaric acid, epigallocatechin gallate, myricetin, apigenin, quercetin-3-O-(caffeoyl)-glucoside and quercetin present in this extract might be responsible for the antioxidant and antimicrobial activity of 30% ethanol extract.