Milk thistle (Silibum marianum) has been known for more than 2,000 years as a herbal remedy for liver and gallbladder diseases. Silymarin, a complex of flavonolignans derived from the seeds of the milk thistle, contains mainly silybin A, silybin B, taxifolin, isosilybin A, isosilybin B, silichristin A, silidianin. Silybin, the principal flavonoid contained in silymarin and a mixture of almost equal amount of silybin A and silybin B, showed antioxidant, anti-inflammatory and anticarcinogenic properties. The therapeutic effect of silybin on insulin resistance has been reported in both clinical studies and experimental liver injury models. However, it has not been investigated whether silybin affects insulin secretion from pancreatic β cells. The present study was, thereby, conducted to investigate the effects of silybin on insulin secretion from MIN6 mouse pancreatic β-cell line. Silymarin and silybin suppressed glucose (3 mM, 25 mM)-stimulated insulin secretion from MIN6 cells in a concentration dependent manner (10 - 100 μM). On the other hand, silymarin and silybin enhanced glibenclamide-induced insulin secretion of MIN6 cells. We now try to clarify the mechanism by which silymarin and silybin affect insulin secretion in MIN6 cells