The present invention provides a stabilization method, a preservation method and the like method of reduced coenzyme Q10, which is useful as functional nutritive foods, specific health foods and the like. Furthermore, the present invention provides a method for efficiently obtaining reduced coenzyme Q10 of high quality and by a method suitable for a commercial production. It is possible to handle and stably preserve reduced coenzyme Q10 under a condition that oxidation by a molecular oxygen is inhibited by contacting reduced coenzyme Q10 with, an ascorbic acid and citric acid or a related compound thereof, and thus a stabilized composition is obtained. Moreover, reduced coenzyme Q10 is converted into a crystalline state in such a condition that the formation of oxidized coenzyme Q10 as a byproduct is minimized by crystallizing reduced coenzyme Q10 in the presence of ascorbic acid or a related compound thereof etc., and thus a reduced coenzyme Q10 crystal of high quality is produced. Furthermore, by successively crystallizing the generated reduced coenzyme Q10 in the presence of ascorbic acid or related compound thereof after reducing oxidized coenzyme Q10 to reduced coenzyme Q10 using ascorbic acid or a related compound thereof, operations are simplified and minimized, and thus reduced coenzyme Q10 of high quality is produced.
