Abstract: Huangguogan is a natural hybrid of tangerine and orange. In this experiment, five-year-old Huangguogan trees were used as the study materials. We established nine different calcium treatments to study the effects of antioxidant enzyme activities (CAT, POD and SOD) on the later stage of the Huangguogan fruit maturation period. Results showed that calcium content in Huangguogan leaf, peel and pulp were increased by spraying calcium on the foliage and fruit surfaces, and were significantly higher than that in CK. After calcium treatment, the antioxidant enzyme activities of Huangguogan fruit were also significantly higher than those in CK. Ten days after fruit ripening, CAT and SOD activities peaked and then decreased rapidly. The POD activity was significantly lower than that in CK during fruit ripening, but always maintained a high level. Calcium was shown to effectively regulate the activities of three antioxidant enzymes and enhanced the reactive oxygen species scavenging capacity in Huangguogan fruits. Comprehensive comparison among the effects of different calcium treatments indicated that calcium chloride (1.0 g/L) was the most effective at regulating the activities of the three antioxidant enzymes.