We investigated the diffusion phenomena of Ti in Nb film prepared with a r. f. magnetron sputtering method. The in-situ observation with Auger electron spectroscopy (AES) showed that Ti appeared on the surface of Nb film on Ti deposited Cu substrate by heating the sample at more than 748K in a high vacuum. The diffusion coefficient of Ti in Nb film was estimated by the AES observation of the Ti diffusion onto the surface of Nb film. It was found that the diffusion coefficient of Ti in Nb film was about 10⁵ times as large as that in Nb bulk. We considered that this mechanism was due to the diffusion of Ti at the interface of nodule in Nb film.