The vibrational relaxation of the OH/OD stretching mode of phenol and its cluster with Ar or H₂O has been observed directry by nanosecond IR-UV pump-probe spectroscopy. The OH/OD vibrational level was prepared bu a tunable nanosecond IR light pulse, and the decay of the pumped level as well as the rise of the relaxed level were observed by two-photon ionization with a tunable UV laser. For the OH stretch level of phenol-d₀, two components were observed: a fast component with a decay time of a few nanoseconds and a slow component with a decay time longer than 1 μs. It was also found that the intramolecular vibrational redistribution (IVR) of the OH stretching vibration of bare phenol-d₀ is classified as intermediate-strong-coupling case. For phenol-d₁, only the slow component was identified for the decay of the OD stretching vibration, whereas the relaxed level showed a rise with a few nanoseconds, similar to the case of phenol-d₀. In the case of phenol-Ar and phenol-H₂O, on the other hand, the OH stretching level showed a fast single-exponential decay curve, indicating a transformation from intermediate coupling to the statistical limit upon the cluster formation.