The study aimed at defining methods  of estimating the content of β-Glucans in the products of barley grain milling by measuring the viscosity of their hydrous and acidic extracts. It was identified the effect of some selected methods of extraction and of sample preparation to extraction on the absolute viscosity of obtained extracts. The viscosity of extracts was measured using an Ostwald viscometer. It was proved that the absolute viscosity of acidic extracts of the barley grain milling products constituted a better index of β-Glucans content in barley products than the absolute viscosity of their hydrous extracts. It was also stated that this method of measuring the viscosity of acidic extracts can be used to estimate a content of β-Glucans in the barley grain milling products provided that the following procedure principles are kept: the size of particles in a sample for which the β-Glucans content is to be determined should be = 150 p.m; the concentration of acidic extracts of barley products should equal lg/10ml; the absolute viscosity of acidic extracts should be measured directly after the extracts have been obtained.