Abstract: A fermented milk product containing Bifidobacterium longum and isomalto oligosaccharide is fermented by Bifidobacterium longum, Lactobacillus delbrueckii subsp. Bulgaricus, and Streptococcus thermophilus, and added isomalto oligosaccharide to promote the growth Bifidobacterium longum and to be the sweetener of the product. The process for producing the fermented milk product comprises adding isomalto oligosaccharide into milk, after mixing the isomalto oligosaccharide and the milk, inoculating the resulting mixture with Bifidobacterium longum as the main fermenting agent, together with Lactobacillus delbrueckii subsp. Bulgaricus and Streptococcus thermophilus, and then carrying out filling, fermenting, and ripening to obtained the fermented milk product of the invention.