Abstract <p><i>Silybum marianum</i> (L.) Gaertner, commonly known as Milk Thistle, is a medicinal plant of the Asteraceae family, valued for its bioactive flavonolignans, particularly silybin (A + B). Despite its widespread distribution, limited research has explored the impact of diverse climatic conditions on its phytochemical properties especially on wild populations that evolved under diverse climatic conditions. This study examined the effects of climatic parameters on the phytochemical composition of <i>S. marianum</i> seeds collected from various geographical regions. The findings revealed substantial variation in silybin (A + B) content among wild populations. Seeds from Gorgan, characterized by high soil temperatures and moderate rainfall, exhibited the highest silybin content (0.06 mg/g dry weight), whereas Ardabil seed population, with its cold climate and high altitude, had the lowest content (0.018 mg/g dry weight). In contrast, phenolic and flavonoid compounds and antioxidant activity were highest in Ardabil seeds population, indicating enhanced biosynthesis of secondary metabolites in response to cooler temperatures and higher altitudes. Fatty acid composition also varied, with Ardabil seeds population containing more saturated fatty acids and Gorgan seeds population showing a higher proportion of unsaturated fatty acids. Additionally, drought stress significantly increased silybin content (A + B) while reducing phenol and flavonoid levels, highlighting an adaptive response to environmental stressors. This study underscores the significant influence of climatic factors on the phytochemical profiles of <i>S. marianum</i>. These insights are crucial for optimizing its cultivation and maximizing its medicinal potential.</p>