Silybum marianum (Milk thistle), a member of the Asteraceae family, is a tall herb with large prickly whiteveined green leaves and a reddish-purple ower that ends in sharp spines. Certain phytoconstituents were revealed such as silybin A, silybin B, isosilybin A, isosilybin B, silychristin, silydianin, apigenin 7-O-β-(2″-O-α-rhamnosyl)galacturonide, kaempferol 3-O-α-rhamnoside-7-O-β-galacturonide, apigenin 7-O-β-glucuronide, apigenin 7-O-β-glucoside, apigenin 7-O-β-galactoside, kaempferol-3-O-α-rhamnoside, kaempferol, taxifolin and quercetin. The plant is exclusively used as anti-diabetic, hepatoprotective,hypocholesterolaemic, anti-hypertensive, anti-inflammatory, anti-cancer, and as an anti-oxidant. Seeds of the plant are also used as an anti-spasmodic, neuroprotective, anti-viral, immunomodulant, cardioprotective, demulcent and anti-haemorrhagic. The plant is also serves as a galactagogue and used in the treatment of uterine disorders. This review paper focuses mainly on phytochemistry and pharmacological activities of the legendary plant milk thistle.