Papaya seeds which make up 8 % to 15 % of fresh fruit weight, are rich source of proteins, crude fibers, fatty acid, calcium, and phosphorus. The aim of this study is to determine the composition of papaya seed oil, to evaluate the antioxidant activity of defatted-papaya seed residue, and to optimize the phenolic compound extracted from defatted-papaya seed residue. The papaya seed oil contained high level of oleic acid (73.79 %), and other acids such as palmitic (14.38 %), stearic (3.58 %), linoleic (1.06 %). The oil yield of ultrasound-assisted extraction method reached 30.24 wt% which was higher than other extracting methods. The antioxidant activity of defatted-papaya seed extraction was evaluated using DPPH method. The results showed that the IC50 values of 67.81 µg/mL and total polyphenol content of 33.99 mg GAE/g. The optimization of extraction conditions was obtained from the orthogonal quadratic experimental model. The highest total polyphenol concentration reached 37.34 mg GAE/g when extracting the papaya seeds by sonicating for 34.2 min, at 46.23 C with the solvent/solid ratio of 14:1.