Eggplant (Solanum melongena L.) is one of vegetables having a potential source of natural antioxidants since it contains bioactive compounds such as phenolics and flavonoids. This research was aimed to study effect of ethanol and water on antioxidant characteristics of eggplant extracts and its application in guava juice to produce a composite juice which may improve antioxidant activity of guava juice. Eggplant was extracted using reflux and maceration methods using water and six different ethanol concentrations (50, 60, 70, 80, 90, and 95% ethanol). Eggplant extracts from each treatment were assessed for total phenolic, total flavonoid, vitamin C contents, and antioxidant activity. The best extract from each extraction method was qualitatively assayed the phytochemical constituents, and incorporated to guava juice. Extraction using ethanol 95% produced extracts with the highest antioxidant activities of 187.83±2.30 and 245.88±1.46 ppm for reflux and maceration methods, respectively. This extract was then mixed with guava juice formulated with predetermined IC50 (50, 100, 150, 200, and 250 ppm) as targets i.e. expected to be reached in final composite juice products, and compared to control and commercial guava juices. Composite juice products of 50 ppm target IC50 and formulated with the reflux and maceration extracts exhibited the highest antioxidant activities, respectively, of 190.61±6.07 and 249.42±1.56 ppm, and was significantly higher than control and commercial juices. Hedonic test showed that composite juice products with refluxed extract of all target IC50 exhibited not-significantly different acceptability in terms of color, aroma, overall, except for taste. Composite juice products with macerated extract were not significantly different in terms of color, aroma, and taste. Although commercial juice has showed a higher acceptance for overall sensories, composite juice products with refluxed and macerated extracts had good acceptance with score 5 (scale of 7) which was comparable to control and commercial juices. Overall, eggplant extracts improved about 10-14 times of antioxidant activities in the composite juice product as compared to control and commercial ones, respectively