A process for preparing (per)fluorohalogenethers having general formula: wherein: A and A′, equal to or different from each other, are selected among Cl, Br and H; m=1, 2; n=0, 1; R′ is a C1 to C3 (per)fluoroalkyl substituent; R is a (per)fluoropolyether substituent; z and z′ are 1 or zero, X1=F, CF3; by reaction of carbonyl compounds having formula: (R′)n—C(O)(F)q(CFX1(CF2)z(CH2)z′OR1)  (II) wherein: R′ and n are as above; q=0, 1; X1=F or CF3; z=0 or 1; R1 is a (per)fluoropolyether substituent; in liquid phase, with elemental fluorine and with olefinic compounds of formula: CAF=CA′F2   (III) wherein A and A′ are as above, at temperatures from −120° C. to −20° C., preferably from −100° C. to −40° C.