The present invention provides a method for stabilizing reduced coenzyme Q
10
, which is useful as a food, nutritional product, nutritional supplement, animal drug, drink, feed, cosmetic, pharmaceutical product, therapeutic drug, prophylactic drug and the like. The present invention also provides a method of producing a reduced coenzyme Q
10
-containing composition which includes the co-presence of reduced coenzyme Q
10
and reduced coenzyme Q
9
and/or reduced coenzyme Q
11
.