In this study, the milk thistle (Silybum marianum Gaertn L.), widespread in Palestine, was selected to study the basic qualitative chemical composition of aqueous, ethanol, chloroform, and hexane extracts from its seeds, and to identify the active compounds present. The results of the phytochemical analysis showed that the seeds of the plant (Silybum marianum Gaertn L.) contain a full range of chemically active compounds in all its extracts, such as: flavonoids, amino acids, carbohydrates, sterols, saponins, anthraquinones, phenolic compounds, steroids, terpenoids, tannins, alkaloids, anthocyanins, quinones, and glycosides. For the first time in Palestine, seventeen amino acids were identified in Silybum marianum Gaertn L. plant seeds using phytochemical analysis, paper and thin-layer chromatography, and standard amino acid assays. As a result of the phytochemical analysis, a range of amino acids were identified in the plant seeds, including: arginine, leucine, valine, lysine, phenylalanine, isoleucine, threonine, histidine, glutamic acid, glycine, serine, proline, aspartic acid, alanine, tyrosine, methionine, cysteine.