The tubers of Jerusalem artichoke (Helianthus tuberosus L.) and Yacon (Polymnia sonchifolia Poepp. et Endll or P. edulis Wedd) were extracted with 80% ethanol, respectively. The oligosaccharide-fraction recovered from each extract was subjected to gel permeation chromatography to reveal the distribution of DP. In addition to a series of fructo-oligosaccharides, glucose and fructose were detected in the fraction from Yacon, but not form Jerusalem artichoke. Yacon and Jerusalem artichoke were stored for a few months, respectively. It was found in Yacon that glucose and fructose increased in amount, and that oligosaccharides decreased. In Jerusalem artichoke, however,oligosaccharides having lower DP were found to increase with a decrease in higher oligosaccharides. Neither glucose nor fructose was detected in Jerusalem artichoke even after a few months storage. No inulo-oligosaccharide was detected in either extract. These findings suggest that both inulin hydrolases are exo-type, and have a different substrate affinity: compared with that from Jerusalem artichoke, the one from Yacon has a rather high affinity to the oligosaccharides having glower DP. From these results, Jerusalem artichoke may well be a better source of fructo-oligosaccharides as foodstuff than Yacon