The hyperfine interaction of140Ce in nickel has been investigated by the time-differential perturbed-angular-correlation technique (TDPAC). The probe was produced by isotope separator implantation of the fission product140Xe, the β- decay chain of which finally populates excited states of140Ce. Different spin rotation spectra were observed before and after an 8 h annealing at 415°C. The analysis of the spectra led to the conclusion that the Ce ions were in the diamagnetic 4+ state. The dominant contributions to the hyperfine interaction are two different magnetic hyperfine fields: |H; hf; 1|=385±7 kOe and |H; hf; 2|=276±12 kOe.H; hf; 1 disappears after annealing. The fraction of nuclei which observeH; hf; 2 is increased by the annealing procedure from 16% to 75%. It is assumed thatH; hf; 1 is the hyperfine field of CeNi in an unperturbed substitutional site andH; hf; 2 is attributed to Ce ions which have trapped a single vacancy.