Extract of Portulaca oleracea seeds is considered important for drug development. Gamma radiation is a form of ionizing radiation that affects plant cells at different rates depending on the dosage, radio- sensitivity, types of plants, and physiological condition of plants. This work aimed to study the effect of gamma radiation with different doses (3, 5, 7, 9, and 11 KGy) on phenolic compounds, superoxide dismutase enzyme activity, chemical composition, and molecular structure of Portulaca oleracea seeds. The results show that gamma radiation significantly affected phenolic and flavonoid contents which increased at 3, 5 KGy, but decreased at 7, 9, and 11 KGy gradually. Tannin content increased at 3, 5, and 7 KGy but decreased at 7, 9, and 11 KGy. Superoxide dismutase activity increased gradually. The carbohydrates decreased and protein content also varied after exposure to gamma radiation. The radiation affected the arrangement, size, interconnection, and orientation of the seeds molecules