Process for preparing lactose-free skimmed, partially skimmed and whole milk, comprising the following steps: 1) pasteurization and skimming, 2) enzymatic hydrolysis of the skimmed milk by lactase enzyme, 3) microfiltration of the hydrolysed skimmed milk and obtainment of a microfiltration retentate (RMF) and of a microfiltration permeate (PMF), 4) PMF ultrafiltration and obtainment of an ultrafiltration retentate (RUF) and of an ultrafiltration permeate (PUF), 5) first PUF nanofiltration and obtainment of the first nanofiltration retentate (RNF l) and of a first nanofiltration permeate (PNF l), 6) second PNF l nanofiltration and obtainment of a second nanofiltration retentate (RNF2) and of a second nanofiltration permeate (PNF2), and 7) final step: obtainment of lactose-free milk by mixing one or more of the fractions deriving from one or more of the previous steps, which is characterized in that: (I) the first nanofiltration of step 5) is carried out with membranes having a molecular weight cut-off ranging from 400 to 600 Da and the second nanofiltration is carried out with membranes having a molecular weight cut-off ranging from 150 to 250 Da, and (II) the final step 7) is carried out by mixing a composition comprising at least RUF, RNFl and PNF2.Linvention concerne un procédé de préparation de lait écrémé, partiellement écrémé et entier sans lactose, comprenant les étapes suivantes : 1) pasteurisation et écrémage, 2) hydrolyse enzymatique du lait écrémé par une enzyme de type lactase, 3) microfiltration du lait écrémé hydrolysé et obtention dun rétentat de microfiltration (RMF) et dun perméat de microfiltration (PMF), 4) ultrafiltration du PMF et obtention dun rétentat dultrafiltration (RUF) et dun perméat dultrafiltration (PUF), 5) première nanofiltration du PUF et obtention dun premier rétentat de nanofiltration (RNF 1) et dun premier perméat de nanofiltration (PNF 1), 6) seconde nanofiltration du PNF 1 et obtention dun second rétentat de nanofiltration (RNF 2
