The studies of ultrafiltration and diafiltration of aqueous solutions of sulphate lignin from Solombal'skii Pulp and Paper Mill, and of effluents after biological and chemical treatment were carried out. It is shown that there is maximum lignin retention of model solutions and effluents on the membranes like Ripor-4. The influence of lignin concentration on their retention on Ripor-4 membranes is studied. The molecular weights of the compounds retained on Ripor-4 membranes and passed through it are determined. The comparison of developed methods with weight method was made using the sulphate effluents after biological and chemical treatment. It is shown tha, when lignin of Solombal'skii Mill is used as a prototype, membrane and weight method give identical results.