The present invention relates to a method of conveniently and efficiently producing reduced coenzyme Q.sub.10 having excellent qualities which is useful in foods, functional nutritive foods, specific health foods, nutritional supplements, nutrients, drinks, feeds, animal drugs, cosmetics, medicines, remedies, preventive drugs, etc. This method is suitable for industrial production thereof.In a method of synthesizing reduced coenzyme Q.sub.10 by reducing oxidized coenzyme Q.sub.10, followed by crystallization, at least one species selected from among hydrocarbons, fatty acid esters, ethers and nitrites is used as a solvent. Thus, the reduced coenzyme Q.sub.10 can be protected from oxidation, and as a result, the formation of the oxidized coenzyme Q.sub.10 as a by-product can be minimized, thereby giving reduced coenzyme Q.sub.10 having excellent qualities.