The invention relates to a process for treating keratin fibres, in particular human keratin fibres such as the hair, comprising: (i) a step of applying an oxidized polysaccharide, (ii) a step of heating to a temperature of at least 100° C., (iii) a step of applying a pyridinedicarboxylic acid compound. The process makes it possible to obtain good hair-conditioning cosmetic properties, with a long-lasting effect. The invention also relates to a cosmetic composition and a kit used for performing the treatment process.