Abstract: AimTo study the NMR phenomena of cetirizine hydrochloride and assign all proton and carbon signals in NMR spectra.MethodsTo record the 1D and 2D NMR spectra of cetirizine hydrochloride while changing the experimental temperature and adding D₂O into the solution.ResultsMore than one NMR signal or broad peak resulting from piperazine and the attached groups with N atom were given in DMSO-d6 solution at room temperature.“Coalescence” or narrowing had occurred for the proton and carbon signals when the experimental temperature was increased or D₂O was added into the solution.ConclusionCompared with the NMR “time scale”, there are more than one conformation of cetirizine hydrochloride in DMSO-d6 solution at room temperature.The different conformation will be exchanged fast while temperature rised and the stable conformation will be existed while D₂O was added into the solution.