This study examined the antioxidant activities of the two Papaver rhoeas L. (PR; PRP (pink flower PR), PRR (red flower PR)) on hydrogen peroxide (H2O2)-induced oxidative stress in HepG2 cells. Different parts (whole, leaf, and fruit) of PRP and PRR were extracted with 50% ethanol. Their antioxidant activities were analyzed using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzoline-6-sulfonic acid) (ABTS) radical scavenging assay. The extracts were evaluated for cellular anti-oxidation and protection from the cell viability, intracellular reactive oxygen species (ROS) scavenging activity and antioxidant enzyme activities. The PR leaf and fruit extracts contained high amounts of bio-active compounds, such as total phenol and total flavonoid. The DPPH and ABTS results revealed antioxidant activity in the following order: leaf, fruit, and whole plant. The pretreatment with all the PR extracts increased the viability, antioxidant enzyme activities and intracellular ROS scavenging activity in a dose-dependent manner in H2O2-treated HepG2 cells. In particular, intracellular ROS scavenging activity was highest using the leaf extracts. These results suggest that 50% ethanol extracts of PR could be used as functional food sources.