Abstract Soymilk was produced from vegetable soybean and fermented by probiotics (Lactobacillus acidophilus La-5, Bifidobacterium animalis Bb-12) in co-culture with Streptococcus thermophilus. The composition of the fermented beverage and oligosaccharides content were determined. The effect of fructooligosaccharides and inulin on the fermentation time and viability of probiotic microorganisms throughout 28 days of storage at 5 °C were evaluated. The soymilk from vegetable soybeans was fermented in just 3.2 h, when pH reached 4.8. Fermentation reduced the contents of stachyose and raffinose in soymilk. Prebiotics had no effect on acidification rate and on viability of B. animalis and S. thermophilus in the fermented beverage. The viable counts of B. animalis Bb-12 remained above 108 CFU mL-1 in the fermented soymilk during 28 days of storage at 5 °C while L. acidophilus La-5 was decreased by 1 log CFU mL-1. The fermented soymilk from vegetable soybeans showed to be a good food matrix to deliver probiotic bacteria, as well as a soy product with a lower content of non-digestible oligosaccharides.