The antioxidant capacities (IC50 values) in the seed and peel from the 4 Royal Project’s fruits extracted under each optimum extraction time were compared. As result shown in Table 2, papaya and muskmelon peel extracts had significantly highest antioxidant potential in which the IC50 value was equivalent to 0.75±0.01 mg mL-1 and 1.20±0.03 mg mL-1, respectively. These 2 values were significantly higher about 10 times than BHT. As previous report, Leong and Shui, 2002 found that papaya have higher primary antioxidant potential, as measured by scavenging DPPH and iron (III) reducing assays. In our experiment, it can be summarized that papaya peels and muskmelon peel could be an alternative source for efficient antioxidant extraction.