Parthenium hysterophorus L. (Asteraceae) grows in Yemen and is widely used by the local people to treat various diseases including rheumatic pain and cold. There is a lack of pharmacognostic, phytochemical, and pharmacological information about this plant in the available literature, so the present research aims to evaluate the pharmacognostic characteristics, chemical constitution, and antioxidant activity of extracts obtained from the aerial parts. The macroscopic and microscopic characteristics as well as physicochemical parameter were established; phytochemicals such as carbohydrates, amino acid, protein, saponins, triterpenes, sterols, polyphenols, flavonoids and alkaloids were identified in the studied extracts. The total phenolic content was 121.00, 95.30 mg/g in 80% methanol and water extracts respectively, but the total flavonoid content was 81.85, 23.00 mg/g in 80% methanol and water extracts respectively. TLC profile was performed for petroleum ether, 80% methanol and water extracts as well as for the chloroform and ethyl acetate fractions obtained from the 80% methanol extract. Ethyl acetate and chloroform fractions were exhibited antioxidant activity by dot-blot DPPH method and by TLC bioautography assay. The antioxidant activity was 28.74±5.21 % and 78.77±4.40 % for the chloroform and ethyl acetate fractions respectively. The aerial parts of Pisadia punctulata are considered a promising candidate for the production of natural antioxidant agents due to the many compounds they contain.