Orange juice is a well-accepted fruit juice, and is a natural source of various vitamins, especially vitamin C, as well as sugar, potassium, thiamine, folate, flavonoids and antioxidants. The respective fructose, glucose, and sucrose concentrations were 9.3, 22.9, and 48.1 g/L in the original orange juice used in this study, and 183.4, 170.1, and 142.8 g/L after concentration. Over 97% of the sucrose in the juice was enzymatically converted to glucooligosaccharides upon addition of 3 U/mL dextransucrase, prepared from Leuconostoc mesenteroides 512FMCM, at 16°C. The synthesized oligosaccharides comprised 35.0% of the total saccharides in the concentrated juice and 31.7% in the original juice. The optimum conditions for oligosaccharide synthesis using the concentrated juice were 35.2 × 10−1 U/mL dextransucrase and 1% Ca(OH)2. The calories in the original and modified concentrated orange juices were 325.4 and 246.7 kcal/L, respectively. Compared to the original concentrated juice, the enzyme-modified concentrated juice prevented the formation of 62.7% of the insoluble glucan resulting from addition of mutansucrase, produced by Streptococcus mutans.