Fructans, just like cellulose, are not digested in the gastrointestinal tract. The reason is that there are no enzymes in the gastric, pancreatic and intestinal juices, which hydrolyze the β-2,1 glycoside bonds. However, they are partially hydrolyzed under the acidic conditions. The objective of this study was the hydrolysis of fructans under the conditions, which simulate the effects of gastric juice. The 30 to 180 minute lasting hydrolysis was conducted at a temperature ranging between 36.6 and 37.0°C, at ph equalling 2. In the case when chicory meal was used, pepsin was also applied. The commercial preparations of FOS (FOS Wako Pure, Raftilose) were applied for the hydrolysis, as well as preparations supplied by the Łódź University of Technology, i.e.: FOS PŁ, crystalline inulin from chicory, chicory dry pulp, nystose, and sucrose. The composition of the preparations before and after the hydrolysis was determined using a HPLC method. It was stated that the kinetic constant of the hydrolysis of fructan, determined according to the mechanism of a one-molecule reaction, ranged from 0.0006 to 0.0035. The following inulin types showed the highest resistance towards the hydrolysis: crystalline inulin and inulin contained in the chicory meal. After a 180 minute period of the hydrolysis, the amount of crystalline inulin was 95%, and of the inulin contained in the not much processed chicory meal: 93%. Preparations containing homogenous β-fructooligosaccharides (Raftilose) and oligomers with DP equalling 3 to 4 (FOS Wako Pure, FOS-PŁ) hydrolyzed the best. The highest amounts (up to 30%) of hydrolyzed saccharides were released during the hydrolysis of the preparations Wako Pure and FOS-PŁ; in these preparations, the key FOS components were: kestose, nystose, and fructosyl-nystose).