Plants have an excellent ability to take up and gather heavy metals from their ambient surrounding. It is a well known fact that high level of heavy metals affects different physiological and metabolic processes in plants. In the present study, changes in soluble peroxidase and ionically bound cell wall peroxidase activity along with accumulation of copper (Cu) in seedlings of Brassica juncea (L.) Czern. were investigated. It was found that Cu inhibited root growth and reduced fresh biomass, while increased soluble peroxidase, ionically bound cell wall peroxidase activity and metal accumulation in roots. Through present study, it is concluded that root growth inhibition by Cu is associated with increment in metal accumulation in seedlings that induced metabolic adaptations to heavy-metal stress.