Milk thistle seed extract (Silbanummarianum), is a mixture of flavonolignans. The main active ingredients in S. marianum are silybin (silibinin), sylichrisitn, and silydianin, commonly referred to collectively as Sylimarin.  Studies showed that Silymarin has anti-inflammatory and antioxidant properties. Seventy-two pregnant female Wister rats were randomly assigned to 3 study groups (24 rats in each group). Group 1, or a control group (C group), received drinking water daily for 14 days from the 8th day of gestation until the delivery. Group 2 (M) and Group 3 (S) received Metoclopramide (5mg\kg\day) and S. marianum seed extract (200 mg\kg\day), respectively, for 14 days. Dams' body weights were monitored throughout the pregnancy. The weights of the newborns in the litter (which previously adjusted to 8 offsprings) were measured on the first day of parturition, and 8 dams from each group were randomly selected and sacrificed. Pregnant female rats in (S) group had litter of significantly higher body weight and increase serum prolactin level in pregnant female rats (p< 0.05). Milk thistle seed extract led to a marked hyperplasia in mammary gland tissue, with strong expression of prolactin receptors. Wister ratsinS. marianum and Metoclopramide groups showed significant increase in serum prolactin levels, had heavier offsprings, and histological and immunohistochemistry changes as compared to the animals that stopped receiving the treatment in the same group (p<0.05). We concluded that S. marianum enhances milk production and mammary gland development (galactogogues effect).