The toxic and corrosive mineral acids are used traditionally in the processes of plant polysaccharides hydrolysis. The use of solid acid catalysts improves the environmental safety of hydrolysis processes and simplifies the separation of the catalyst from the reaction products. The stability of solid acid catalysts based on mesoporous SBA-15 and graphite-like carbon material Sibunit-4, containing SO₃H– groups, in the process of larch arabinogalactan hydrolysis at 150 ° С was studied. The compositions of the resulting hydrolysates were investigated by gas chromatography. It was established that acid-modified Sibunit-4 does not lose the catalytic activity after three cycles of hydrolysis process for a total duration of 12 hours. Modified SBA-15 catalyst was less stable at the studied conditions. The decrease of monosaccharides concentration in the hydrolysates, the changes in the structure of the catalyst and 40 % loss of its weight were found after the third cycle of larch arabinogalactan hydrolysis.