The ultrafast relaxation dynamics of a widely used viscosity probe molecule, auramine 0 (AuO), was investigated in water and a water/aerosol-OT (AOT)/n-heptane reversed micelle. We discussed the contribution of specific interactions between AuO and the local environment to the relaxation dynamics. The transient absorption spectra of AuO showed that the nonradiative, relaxation process of the photoexcited AuO in the AOT-reversed micelle was approximately I order slower than that in bulk water and the relaxation rate decreased with a decrease of the size of the reversed micelle. The slowing down of the relaxation was attributed to a depletion of the ultrafast solvation dynamics of water molecules in the interfacial area of the reversed micelle as well as an increase of viscosity, which strongly suggested that the viscosity of the reversed micelle determined from the fluorescence yield of AuO was somewhat overestimated. In addition, it was observed that the absorption coefficient of the twisted intramolecular charge transfer-like (TICT-like) intermediate state of the AuO in the reversed micelle was about half as large as that in bulk water. A decrease of the refractive index of the TICT-like state was also observed in the reversed micelle by the ultrafast transient lens measurements. The reduction of both the absorption coefficient and the refractive index of the TICT-like state indicated a considerable change of the molecular structure or the charge distribution of the TICT-like state. Such a change of the TICT-like state suggested the existence of strong interactions between AuO and AOT. These interactions would also affect the relaxation dynamics and the fluorescence yield of the AuO in the reversed micelle.