A process for treating fibroses including administering a therapeutically effective amount of a pharmaceutical composition which includes at least one biocompatible polymer of the following general formula (I): AaXxYy wherein: A represents a monomer selected from the group consisting of a sugar or —(O—CH2—CH2—CO)—, X represents a carboxyl group bonded to monomer A and is contained within a group according to the following formula: —R—COO—R′, in which R is a bond or an aliphatic hydrocarbon chain, optionally branched and/or unsaturated, and which can contain one or more aromatic rings except for benzylamine and benzylamine sulfonate, and R′ represents a hydrogen atom or a cation, Y represents a sulfate or sulfonate group bonded to monomer A and is contained within a group according to one of the following formulas: —R—O—SO3—R′, —R—N—SO3—R′, —R—SO3—R′, in which R is a bond or an aliphatic hydrocarbon chain, optionally branched and/or unsaturated, and which can contain one or more aromatic rings except for benzylamine and benzylamine sulfonate, and R′ represents a hydrogen atom or a cation, a represents the number of monomers A such that the mass of the polymers of formula (I) is greater than approximately 5,000 da, x represents a substitution rate of the monomers A by the groups X, which is between approximately 20 and 150%, and y represents a substitution rate of the monomers A by the groups Y, which is between approximately 30 and 150%.