To produce isomaltooligosaccharides having maltose linkages, an acceptor reaction with sucrose and maltose as a co-substrate was conducted through the batch fermentation process using Leuconostoc mesenteroides ATCC 13146. During fermentation the size distribution of isomaltooligosaccharides changed continuously, finally reaching the steady state at the end of fermentation. Compositional analysis showed major isomaltooligosaccharides produced were composed of degree of polymerization (DP) 3 [parmose or alpha-D-glucopyranosyl-(1 --> 6)-D-maltose], DP 4, and DP 5, all being branched form. Portion of DP 3 was about 90% at the beginning of fermentation, then decreased rapidly to 40%. Presumably, most DP3 at the initial stage was used as acceptors for synthesizing larger oligosaccharides. At the stationary growth phase, the amount of oligosaccharides reached maximum after 15-hr fermentation, and yield and specific yield of total oligosaccharides were 77.4% of theoretical yield and 38.7 g/L/g cell mass, respectively. Yields of DP 3, 4, and 5 were 38.1, 27.2, and 12.2%, respectively.