A method is presented for synthesizing thermo-, acid-stable oligosaccharides (TASO) from sucrose (2.5–4 M) using a dextransucrase prepared from Leuconostoc mesenteroides B-512FMCM. The degree of polymerization (DP) of oligosaccharides synthesized was from 2 to 11. TASO resisted hydrolysis of its glycosidic linkages at 140 °C and pH 6.0 for 1 h. It was stable at pH’s ranging from 2 to 4 at 120 °C. These oligosaccharides effectively inhibited the formation of insoluble glucan, the growth and acid production of Streptococcus sobrinus. However, it stimulated the growth of probiotic organisms such as Bifidobaterium sp. TASO potentially can be used as sweeteners for the food and beverages where thermo- and acid-stable properties are required and as potential inhibitors of dental caries.