The prickly pear cactus (Opuntia), native to Mexico, has grown in popularity and is locally grown and adapted on Jeju Island. The fruits of this cactus species are in particular widely employed as raw materials, which are then processed into various food and medicinal items, including chocolates and vitamins, for purposes of human consumption. Because this crop has been dubbed one of Jeju’s iconic agricultural crops, research studies elucidating the prickly pear cactus’ medicinal properties, including antioxidant activity, of this particular plant and related cultivated species have demonstrated high value to the scientific community. Currently, consumers do not purchase products f or c onsumption a lone, but in a ddition f or t heir added health benef its. The present study in particular honed in on two species of prickly pear cactus that are cultivated on Jeju Island which include: ‘Baeknyeoncho’ (Opuntia ficus-indica) and ‘Cheonnyeoncho’ (Opuntia humifusa). From these species, s pecif ci p lant p arts i ncluding t he f lower, mature and y oung stems, roots, a nd f ruit w ere subjected to further antioxidant analysis, which included the determination of polyphenol, flavonoid, DPPH radical, ABTS radical, and anthocyanin levels. These particular antioxidants were determined during two seasons, over the course of the summer and winter. Results revealed that the antioxidant activity for both species was more active during the summer season. Antioxidant levels occurred at the highest rates within t he flowers o f the c actus plants. However, of significant note was that the cactus stem, in both mature and young plants, possessed higher antioxidant activity compared to those of the fruit that is currently employed for commercial purposes.