<i>Background:</i> Adult asthma is caused by interaction effects of multiple genetic and environmental factors. Some studies have suggested that antioxidant enzyme activity and gene polymorphisms may play important roles in the context of asthma. Therefore, our study objectives were to investigate the association between asthma, antioxidant activities and the polymorphisms of manganese superoxide dismutase (Mn-SOD) or catalase (CAT). <i>Materials and Methods:</i> A case-control study, for which we recruited 250 asthmatic adults and 250 age- and sex-matched controls. All subjects completed a questionnaire. Waist and hip circumference measurements, a lung function test and DNA genotyping were performed. In total, 50 incident cases and 50 matched controls who were non-smokers or had quit smoking for at least 1 year were selected in order to investigate SOD and CAT activity levels. <i>Results:</i> In our study, we did not find a significant association between Mn-SOD Ala16Val, CAT C–262T and asthma. The level of SOD activity in new-onset asthma patients was significantly lower than in control subjects (p < 0.0005). The level of CAT activity in new-onset asthma patients was significantly higher than in control subjects (p < 0.0005). <i>Conclusions:</i> The levels of SOD and CAT activity were significantly related to adult asthma. SOD and CAT activity may be good tools to differentiate potential asthma sufferers. This would enable us to further investigate the mechanism of defective antioxidant enzymes in the context of asthma pathogenesis.