A process for separating proteins and/or protein fractions from biomass materials, characterized in that the process comprises the steps, where in the first step biomass material containing streams and materials of plant or animal or algal or microbial origin, which contain proteins, or combinations thereof is mixed from 30 min to 30 hours at the temperature from 0°C to 100°C at the pressure 100 mbar - 30 bar with an aqueous deep eutectic solvent comprising a hydrogen bond acceptor selected from alkali metal carboxylates and earth alkaline metal carboxylates having the structure I: m Y n o, where X denotes an alkali metal or earth alkaline metal selected from Na, K, Li, Be, Mg or Ca, preferably Na or K; Y denotes a mono- or polyvalent carboxylate, which may carry a straight alkane chain with a length between 1 and 20 carbons, an aromatic moiety, a branched alkane, a multivalent carboxylic acid, alcohol groups, alkenes and alkynes with chain lengths of 1 to 20 carbon units; m denotes the charge of the alkali or earth alkaline metal ion, +1 or +2; n denotes the number of carboxylate anions, 1 to 2; and o denotes the overall charge of the carboxylate anion, -1 or -2, and urea as hydrogen bond donor, to obtain biomass mixture containing 1 - 40 wt% of the biomass material, calculated based on dry weight, wherein deep eutectic solvent comprises a molar ratio of the alkali metal carboxylate or earth alkaline metal carboxylate to urea from 5:1 to 1:5 and the deep eutectic solvent comprises 0.01 - 4 mol of water with respect to the molar amount of the alkali metal carboxylate or earth alkaline metal carboxylate; in the second step the biomass mixture is separated into a non-solubilized fraction and a liquid fraction, wherein 0 - 100°C water 1 - 8 times the volume of the deep eutectic solvent is added to the biomass mixture, the amount of water also containing the amounts of water possibly present in the first step or originating from the first step; and in the third step proteins are separated from the liquid fraction using technique based on molecular size selected from ultrafiltration, dialysis, membrane filtration methods and combinations thereof to yield a protein solution, or using technique based on isoelectric precipitation to yield a protein precipitate. X denotes an alkali metal or earth alkaline metal selected from Na, K, Li, Be, Mg or Ca, preferably Na or K; Y denotes a mono- or polyvalent carboxylate, which may carry a straight alkane chain with a length between 1 and 20 carbons, an aromatic moiety, a branched alkane, a multivalent carboxylic acid, alcohol groups, alkenes and alkynes with chain lengths of 1 to 20 carbon units; m denotes the charge of the alkali or earth alkaline metal ion, +1 or +2; n denotes the number of carboxylate anions, 1 to 2; and o denotes the overall charge of the carboxylate anion, -1 or -2, and urea as hydrogen bond donor, to obtain biomass mixture containing 1 - 40 wt% of the biomass material, calculated based on dry weight, wherein deep eutectic solvent comprises a molar ratio of the alkali metal carboxylate or earth alkaline metal carboxylate to urea from 5:1 to 1:5 and the deep eutectic solvent comprises 0.01 - 4 mol of water with respect to the molar amount of the alkali metal carboxylate or earth alkaline metal carboxylate; in the second step the biomass mixture is separated into a non-solubilized fraction and a liquid fraction, wherein 0 - 100°C water 1 - 8 times the volume of the deep eutectic solvent is added to the biomass mixture, the amount of water also containing the amounts of water possibly present in the first step or originating from the first step; and in the third step proteins are separated from the liquid fraction using technique based on molecular size selected from ultrafiltration, dialysis, membrane filtration methods and combinations thereof to yield a protein solution, or using technique based on isoelectric precipitation to yield a protein precipitate.