Abstract: Background and Objective: Natural antioxidants are responsible for preventing the deleterious consequences of oxidative stress. Plants not only provide food for man but also provide number of active compounds with potent and varied therapeutical value. The present study was carried out to evaluate the antioxidant activity and quantitative estimation of the total phenolics as Gallic Acid Equivalent (GAE) per gram dry weight and total flavonoid as Quercetin Equivalent (QE) per gram dry weight of Eichhornia crassipes (Pontederiaceae) from methanolic extract of different plant parts (Leaves, petiole and roots). Materials and Methods: The methanol extract of the leaves, petiole and bark of Eichhornia crassipes were estimated for total antioxidant capacity using 1,1-diphenyl picrylhydrazyl (DPPH) free radical scavenging assay, total phenolic and flavonoid contents using spectrophotometric methods. Statistical analysis was performed as Mean±Standard Error Mean (SEM). The IC50 values were also calculated by linear regression analysis. Results: Maximum total phenolic content was recorded in leaves (IC50 value 0.217±0.032 mg g–1 dry weight) and maximum total flavonoid content was found in leaves (IC50 value 0.481±0.023 mg g–1 dry weight) and highest radical scavenging activity was observed in petiole with IC50 value 6.411±0.46 mg mL–1 compared with standard values obtained from gallic acid standard IC50 value 0.516±0.22. Conclusion: It is concluded that the phenolics and flavonoids represent good sources of natural antioxidants. The above results depicted that this plant exhibits significant antioxidant activity.