The aim of the study was to evaluate in what manner rumen bacterium Pseudobutyrivibrio ruminis strain k3 uses and ferments timothy grass fructan, inulin, inulooligosaccharides, sucrose, fructose and glucose. The highest concentration of bacterial population was noted at 12 h of incubation for all cultures except from that on fructose which occurred at 24 h. The highest specific growth rates occurred on sucrose, timothy grass fructan and glucose, whereas the lowest on fructose. Protein productions on timothy grass fructan, glucose, sucrose and inulooligosaccharides were 66.4–73.5 mg/100 ml of culture, while on fructose and inulin – 59.9 and 34.5 mg/100 ml, respectively. Bacteria utilized more than 91% of initial dose of timothy grass fructan, sucrose, glucose, inulooligosaccharides and fructose, and less than 47% of inulin. Production of butyrate on timothy grass fructan, sucrose, inulooligosaccharides and glucose was higher than on fructose. In contrast lactate production on fructose and glucose was higher than on timothy grass fructan and inulooligosaccharides. The lowest production of both acids was on inulin and the highest on fructose, glucose and sucrose. It was stated that Pseudobutyrivibrio ruminis strain k3 was able to use sucrose and fructan of β-2,6-type originated from grasses but possessed limited capability of using inulin.