The International Society of Rare Sugars have defined rare sugars and their derivatives as monosaccharides which are present in limited quantities in nature. Recently， mass enzymatic production of these sugars was established. d-glucose and d-fructose are abundant in nature and act as an energy source， whereas rare sugars are not easily metabolized in living organisms， but possess beneficial effects. In this study， we report on two rare sugars， d-psicose and d-allose， which have been well studied so far. d-psicose is a zero calorie sweetener and has approximately 70 % of the sweetness of sucrose. It has been previously shown that it suppresses postprandial blood glucose elevation by α-glucosidase inhibition and facilitating glucokinase translocation. d-psicose also reduced abdominal fat accumulation through the suppression of lipogenic enzymes in liver. d-allose， an isomer of d-psicose， has approximately 80% of the sweetness of sucrose and has an energy value close to zero. d-allose suppressed the generation of reactive oxygen species and regulated the redox states in various cell lines， which led to the suppression of elevating blood pressure and ischemia-reperfusion injury. d-allose induced thioredoxin interacting protein， involved in specific cell cycles， and consequently suppressed cellular proliferation. Rare sugars are also chemically produced by Lobry de Bruyn-Alberda van Ekenstein transformation. Through this reaction， a sugar syrup consisting of d-glucose， d-fructose and rare sugars can be obtained. An animal study demonstrated the safety of the syrup and that it reduced abdominal fat accumulation. The combination of energy providing sugars and rare sugars might be an ideal approach for preventing metabolic syndrome， although further studies are required. Key words : Rare sugar， d-Psicose， d-Allose， Blood glucose， Abdominal fat， Reactive oxygen species