This study was performed to investigate the increase of S-allylcysteine content, a biomarker of black garlic, during its aging period, as well as the serum lipid-lowering effects of black garlic extract in high fat diet fed rats. The highest content of S-allylcysteine was observed on the 15th day of the aging period. Sensory evaluation was also estimated to be extremely good on the 15th day of the aging period. High fat diet rats with induced hyperlipidemia were fed diets containing black garlic extract of low, medium, and high doses for 6 weeks. No significant difference in body weight gain and food efficiency was observed between normal, placebo and black garlic fed groups. Liver weight was significantly higher in black garlic fed groups than in the normal group. Total serum cholesterol and triglyceride were significantly lower in low, medium, and high dose groups than in the normal group. Also, HDL-cholesterol was significantly higher and LDL-cholesterol was significantly lower in black garlic diet fed groups than in the normal group. Hepatic levels including total lipid and cholesterol were especially decreased in the black garlic diet fed group than in the placebo group. These results suggest that black garlic intake reduces the levels of serum and hepatic cholesterol in high fat diet fed rats. In conclusion, black garlic has a potential to be used as a functional health food ingredient with beneficial effects on lowering cholesterol and triglyceride levels.