Functional rare sugar (RS) is a new-generation sugar substitute with a low calorie. Although many functional studies of RS have been reported, there are few studies on sarcopenia. To investigate the effect of RS in sarcopenia, histopathological and biochemical analyses were performed. The young mice group (YC, 8-week-old), negative old mice group (NC, 12-month-old), and NC+3% (w/w) RS group (RS, 12-month-old) were fed each experimental diet based on AIN-93G for 12 weeks. The RS supplement increased the expression of IGF-1 reduced by aging, while decreased Myostatin expression increased by aging. The expressions of the myogenic transcription factors (Myf5, My6, Myogenin) and the proteins involved in the protein synthesis (Akt, AMPK, PI3K, mTOR, PGC1α) were significantly increased, while muscle-wasting cytokine TNFα protein expression was markedly decreased in the RS group compared to the NC group. As a result, the RS supplement prevented muscle loss caused by aging, increased grip strength, and inhibited the fat accumulation in muscle tissue by AMPK activation. Taken together, the RS could be used as a functional food source for improving aging-associated sarcopenia.