The hypolipidemic activity of leaves of rosemary (Rosmarinus officinalis), a herbal plant was studied. Three groups of BALB/c mice were treated as following: the first group was fed with normal diet (sugar & water), the second group was fed with high cholesterol (HC) (2% by weight) and coconut oil (25% by weight), for 36 days, and the third group was fed with HC diet and given 100 mg/kg rosemary extract (10% w/v) during the last 15 days of treatment period. There was a significant decrease (P < 0.001) in plasma total cholesterol (TC)(-68.57%), low density lipoprotein (LDL) (-56.34%), and triglycerides (TG) (-182.61%). A significant increase in high density lipoprotein (HDL) (38.53%) was obtained in rosemary-fed mice compared to HC mice. In another experiment, the immunomodulatory activity of aqueous extract of R. officinalis was evaluated in BALB/c mice. Mice were treated with three doses of extract (10, 50, 100 mg/kg body weight) for 8 weeks. Humoral immunity against membrane proteins of sheep erythrocytes measured by ELISA showed that IgM (Immunoglobulin M) response significantly increased by 26.95%, 36.5%, 70.78% respectively, in mice fed with 10, 50, and 100 mg/kg of rosemary as compared to the control group (P < 0.05). IgG (Immunoglobulin G) response increased significantly at all antibody titers, in mice fed with rosemary at doses of 10, 50, and 100 mg/kg. Meanwhile, there was no significant different in IgM and IgG responses between 50 and 100 mg/kg (P > 0.05). On the other hand, concanavalin A-stimulated proliferation of spleen cells from mice fed with 100 mg rosemary extract was significantly higher by 57% than that of cells from the corresponding control animals.