The current study was done to examine the impact of ambient air pollution on some biological factors in Prosopis juliflora plants using two sites; control and polluted (around one of the oil fields in south west of Iran). Various morphological and biochemical characteristics of the plants were studied in both sites and compared with each other. Plants exposed to pollution showed lower leaf area, petiole length, chlorophylls, carotenoids and soluble carbohydrate contents as compared to plants growing in control site. Proline levels in polluted leaves significantly increased (p < 0.01), suggesting the activation of protective mechanism in these plants under air pollution stress, and also the observed responses are regarded as adaptive and compensative to the adverse effects of air pollution.