Abstract: The antioxidant activities and total phenolic contents of acetone/methanol extracts from Salvinia molesta and Eichornia crassipes were investigated. The antioxidant activities was evaluated by using scavenging of 2-2-Diphenyl-1-Picrylhydrazyl radical (DPPH·). The Total Phenolic Content (TPC) was evaluated according to the Folin-Ciocaltue assay and gallic acid was used as standard. The Flavonoids Contents (TFC) were evaluated by using the aluminum chloride method. As the result, extract from S. molesta exhibited the highest antioxidant activity with IC50 value of 27.75±0.15 μg mL-1 followed by extract from leaf of E. crassipes (IC50 value of 145.33±0.89 μg mL-1) and petiole of E. crassipes (IC50 value of 179.18±1.54 μg mL-1), repectively. The TPC and TFC of extracts were in the range of 39.58±0.38-69.97±0.38 mg GAE g-1 dw and 12.67±0.02-23.16± 0.08 mg QE g-1 dw, respectively. A High-Performance Liquid Chromatography (HPLC) method with photodiode array detection at 280 nm was used for identification and quantification. Nariginin was the major phenolic compounds (65.56-68.71 mg g-1 of crude extract) found in the extracts followed by myricetin (1.34-17.05 mg g-1 of crude extract) from S. molesta and E. crassipes.