Kien Giang has a diverse ecosystem with many species of plants used as medicine. Ethanol extracts from 14 plant species collected in Kien Giang were evaluated for total polyphenols, flavonoids and total antioxidant activity. Total phenolic content was determined spectrophotometrically according to Folin–Ciocalteu colorimetric method. Total flavonoid content of ethanolic extracts was determined using aluminum chloride colorimetric method. The total antioxidant capacity was evaluated by the phosphomolybdenum method. The results showed that total phenolic content of ethanolic extracts of the investigated plant species ranged from 82.88 to 671.83 mg GAE/g extract, while the total flavonoid contentranged from 139.90 to 563.93 mg QE/g extract. The highest antioxidant activity was shown in the leaf and fruit extracts of Sphaerocoryne affinis (with Abs0.5 value of 36.15 µg/mL; 44.65 µg/mL) that contained the highest concentrations of polyphenols and flavonoids. These plants exhibited strong antioxidant activity and will be potential sources for isolating antioxidants.