The present invention relates to a process for dyeing and relaxing curls of keratin fibres, such as the hair, which comprises the application to the fibres of one or more acidic compositions comprising reducing agents and of one or more compositions comprising hair-dyeing agents, and a step of heat treatment of the fibres by means of a heating tool. A subject of the invention is also the use of the composition(s) comprising reducing agents and of the composition(s) comprising hair-dyeing agents in a process for dyeing and relaxing curls of keratin fibres. Finally, a subject of the invention is a multi-compartment device or “kit” suitable for carrying out such a process.
