We have studied the effect of thymoquinone on the blood levels of cholesterol, triglycerides, HDL and LDL in albino rats. A total of 200 rats, 150 test group and 50 as controls, were included in the study. Six doses of thymoquinone (0.5, 1, 2, 4, 6, and 8 mg/kg/day) were given through intraperitonial injections at 8 Am. The drug was administered for 5 durations 1, 4, 7, 10, and 14 days. Thymoquinone produced significant reduction in the blood level of all parameters studied. There was no linear dose or time dependent effect on these parameters. The effect of thymoquinone started after 4 days with all doses and continued, with some swings, in the rest of the duration. The dose of 8 mg/kg was found to be toxic. It is concluded that thymoquinone has a hypocholestrolemic as well as a reducing effect on triglycrides, HDL and LDL. Therefore, we recommend further research on the therapeutic effect of thymoquinone in related diseases in humans and animals.