A system for mixing two cosmetic products includes a tubular bottle defining a first reservoir containing a first product to be mixed, a tubular cartridge defining a second reservoir containing a second product to be mixed, a retaining device suitable for retaining the cartridge on the bottle in an injection position in which the first reservoir communicates with the second reservoir via the inlet orifice of the base and the injection orifice of the cartridge, a perforator having an upper edge designed to perforate the cap that seals the inlet orifice when the cartridge occupies the injection position, and a piston that seals the lower end of the cartridge and that is axially slidably mounted between an initial bottom position and a final top position in order to push the second product through the injection orifice from the second reservoir to the first reservoir.