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 a 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.
