Abstract: There are provided a hydroquinone-containing whitening agent having high storage stability and sustained release of hydroquinone, a process for production of the whitening agent, and a whitening method for skin which employs the whitening agent. The whitening agent of the invention comprises a crystalline molecular complex composed of hydroquinone or a derivative thereof and a surfactant, wherein formation of the molecular complex improves the storage stability of the hydroquinone-containing whitening agent against heat, oxygen and light, while the hydroquinone is gradually released for a sustained whitening effect of the whitening agent.