The invention concerns a method for obtaining a highly enriched TGF-beta protein fraction in activated form, from a liquid solution rich in proteins said to be soluble in the aqueous phase of milk and/or of whey, said method comprising the following steps; a) adjusting soluble proteins purified at a concentration between 5 and 30 g/liter of solution; b) precipitating part of the whey proteins by acidic treatment of the solution thus obtained to a pH ranging between 4 and 5.5 and at a temperature ranging between 55.degree. C. and 68.degree. C.; c) carrying out a microfiltration of the treated solution by diafiltration, so as to obtain respectively a microfiltration retentate and a microfiltrate; d) recuperating the microfiltration retentate containing the protein fraction highly enriched in TGF-beta; e) drying the microfiltration retentate which has been subjected to diafiltration to obtain a powder highly enriched in TGF-beta.