Background: Plants have a well-developed defensive machinery for minimizing the reactive oxygen species (ROS) associated damages in the form of enzymatic and nonenzymatic antioxidants. The in-vitro mechanism of antioxidant action of plant extracts may involve direct inhibition of the ROS generation or ROS scavenging. The antioxidant activity of the extracts may be due to active constituents alone or the combination of constituents. However, the amount of constituents are known to vary according to the change in environment. Method: In our study, antioxidant activity of Amaranthus caudatus L. from two different sites (elevation sites) was investigated at three stages, (vegetative, pre flowering and post flowering) using ethanolic extract (EtOH). Result: The phenolic and flavonoid content increased at all stages from site 1 to site 2. The total reducing power, Ferrous reducing antioxidative power (FRAP), diphenyl picryl hydrazine (DPPH) radical scavenging assay, superoxide dismutase scavenging (SOD) assay and hydrogen peroxide (H2O2) scavenging activity increased from site 1 to site 2 at all the three stages. Conclusion: The results reveal that the altitude and the growth stage have a significant effect on antioxidative potential of Amaranthus.