Coenzyme Q10 (CoQ10) is a naturally occurring component present in living cells. Its physiological function is to act as an essential cofactor for ATP production, and to perform important antioxidant activities in the body. In most countries, CoQ10 has been widely used as a dietary supplement for more than 20 years. Recently, the use of CoQ10 as a dietary supplement has grown with a corresponding increase in daily dosage. The present review describes the safety profile of CoQ10 on the basis of animal and human data. The published reports concerning safety studies indicate that CoQ10 has low toxicity and does not induce serious adverse effects in humans. The acceptable daily intake (ADI) is 12mg/kg/day, calculated from the no-observed-adverse-effect level (NOAEL) of 1200 mg/kg/day derived from a 52-week chronic toxicity study in rats, i.e., 720 mg/day for a person weighing 60 kg. Risk assessment for CoQ10 based on various clinical trial data indicates that the observed safety level (OSL) for CoQ10 is 1200 mg/day/person. Evidence from pharmacokinetic studies suggest that exogenous CoQ10 does not influence the biosynthesis of endogenous CoQ9/CoQ10 nor does it accumulate into plasma or tissues after cessation of supplementation. Overall, these data from preclinical and clinical studies indicate that CoQ10 is highly safe for use as a dietary supplement. Additionally, analysis of CoQ10 bioavailability or its pharmacokinetics provides the pertinent safety evaluation for CoQ10.