To determine some physiological and biochemical changes in Capsicum annuum L. grown in vitro, the effects of different Cu concentrations on this plant were investigated. Cu was applied in the form of Cu sulfate (CuSO₄) in three levels (0, 0.1, and 0.2 mM) and at three times (days 8, 10, and 12). With Cu treatments, superoxide dismutase (SOD), catalase (CAT) activities, and total phenolic compound amounts increased compared to the control. The protein amount gradually declined with increasing Cu concentrations. This study demonstrated that Capsicum annuum L. is quite tolerant of Cu and mobilizes catalase, superoxide dismutase, and phenolic compounds in order to mitigate Cu-stress damage.