An object of the present invention is to provide a rare sugar-containing composition having improved properties as a sweetener while maintaining the excellent functionality of D-psicose. The invention relates to a method of producing a rare-sugar containing composition with D-fructose as a raw material. An intended product having a novel composition of D-glucose, D-fructose, and D-psicose is obtained by preparing a mixture of D-fructose and D-psicose by using ketose 3-epimerase in the first stage and converting D-fructose into D-glucose by using D-xylose isomerase inert to D-psicose in the second stage. The first-stage product is a mixture of D-fructose and rare sugar D-psicose. The resulting mixture is a sweetener having a taste quality equal to that of sugar.