Milk thistle (MT) or Silybum marianum is a weed that grows in many parts of the world. Since centuries, its seeds are used as herbal remedies for many diseases. In this study, an in- vitro model was designed to mimic the temperature, pH, and the time of passage of seeds through the stomachs and the intestinal tracts of chickens to investigate the absorption capacity of MT seeds for aflatoxin B1 (AFB1). Forty-eight flasks, each containing 25 g of rice and 250 or 500 µg/kg AFB1 in the presence of 125, or 250 mg MT seeds were used in six treatments with two samples and four replicates, I) 250 µg/kg of rice contaminated with AFB1 as the control; II) 500 µg/kg AFB1 as a control; III) 125 mg MT seeds plus 250 µg/kg AFB1; IV) 125 mg MT seeds plus 500 µg/kg AFB1; V) 250 mg of MT seeds plus 250 µg/kg AFB1; VI) 250 mg MT seeds plus 500 µg/kg AFB1. A high proportion of milk thistle was bound by 250 µg/kg of AFB1 in treatment number V. The highest and lowest levels of AFB1, i.e., 331.64±9.57 µg/kg and 45.62±4.25 µg/kg, were determined in treatments II and V, respectively. The mechanism by which MT seeds diminish AFB1 is not fully understood. MT seeds are a rich source of fiber, and therefore, they may have a high capacity for binding to the aflatoxin. On the other hand, silymarin, a component of MT seeds, is a natural polyphenolic flavonoid that has antioxidant properties. Polyunsaturated fatty acids may also act as antioxidants, where by preventing the absorption or bioactivation of mycotoxins by enhancing their metabolism and excretion. It was concluded that the MT seeds were able to effectively diminish AFB1 in vitro.