The invention relates to a process for treating keratin materials such as keratinous fibers, in one or more steps, by applying an ionic liquid, the ionic liquid being obtained by applying the following ingredients: i) one or more derivatives of alpha oxoacid or alpha hydroxy acid of formula (I) and (II) below, and their optical isomers: Formulas (I) and (II) in which R1 represents a hydrogen atom, or an optionally substituted C1-C10 alkyl group, preferably substituted by a group selected from a) hydroxy, b) carboxy, c) an anionic group such as carboxylate -C (O) O-, X +, sulfonate, X +, sulfate, X +, phosphate, X +, phosphonate, X + with X + representing a cationic counterion such as an ammonium ion, a cation derived from an alkali metal or alkaline earth metal, a cyclic or acyclic organic cation d) an ammonium cationic group, Q-, e) a cyclic or acyclic organic group, Q -； with Q- representing anionic counterion such as halide, acetate； Y represents: - a group OZ or O-Z + with Z representing i) a hydrogen atom, ii) a cation derived from an alkali metal, iii) a cation derived from an alkaline earth metal, iv) a ammonium cation, v) a cyclic or acyclic organic cation, vi) a C 1 -C 10 alkyl group optionally substituted with an anionic or cationic group, preferably substituted by a group selected from a) an anionic group such as carboxylate -C (O) ) O-, X +, sulfonate, X +, sulfate, X +, phosphate, X +, phosphonate, X + with X + representing a cationic counterion such as an ammonium ion, a cation derived from an alkali metal or alkaline earth metal, a cyclic organic cation or acyclic b) a cationic ammonium group, Q-)) a cyclic or acyclic organic cationic group Q-； with Q- representing anionic counterion such as halide, acetate； an NR2R3 group with R2 and R3, which may be identical or different, representing a hydrogen atom or an optionally substituted C1-C10 alkyl group, preferably substituted by a group chosen from a) an anionic group such as carboxylate -C (O) ) O-, X
