Sonchus arvensis, a perennial sowthistle, is least explored in Nepal, although several uses like anti inflammatory, sedative and kidney stone eradicating properties have been identified till date. Samples of the plant were collected from Nagarjun Hill, Kathmandu, Nepal. The aerial parts of the plant were dried, crushed, and extracted using a Soxhlet apparatus using petroleum ether, diethyl ether, methanol, and water, each in a stepwise manner. The extracts were concentrated and stored until used for experiments. This study aims at exploring antioxidant and cytotoxic properties of the methanolic extract of this plant. Antioxidant activity was calculated by percentage scavenging activity of acetic acid and that of methanolic extract. The brine shrimp activity was calculated by brine shrimp bioassay. This study revealed that the methanolic extract possessed strong antioxidant activity while petroleum ether, diethyl ether, methanol and water extracts didn’t show cytotoxicity. Thus, it is concluded that the plant possess strong antioxidant properties.