Abstract: At least one enzyme selected from .alpha.-amylase of various types, an oligosaccharide-forming amylase, .beta.-amylase and a debranching enzyme and an enzyme capable of forming nigerooligosaccharide by transglycosylation and/or condensation reaction are allowed to successively or simultaneously act on a material comprised of at least one selected from i) starch, ii) a maltooligosaccharide with a degree of polymerization not lower than maltose and iii) a dextrin, to form nigerooligosaccharide, which is thereafter optionally reduced to obtain a starch sugar composition containing the nigerooligosaccharide or a reduction product thereof. This starch sugar composition may be added to food and drink as at least part of its sweeteners, whereby various advantages can be provided, e.g., not only a sweetness can be imparted, but also the quality of sweetness can be improved, and the moisture retention of foods can be improved.