The present work reports the tracer diffusion coefficient for Nb-93 in rutile TiO2 single crystals using secondary ion mass spectrometry (SIMS). The determined tracer diffusion coefficient exhibited the following temperature dependence in air (p(O-2) = 21 kPa) over the range 1073-1573 K: D-93Nb= (4.7 m(2) s(-1)) x 10(-7 +/- 0.4) exp ((-244 +/- 9 kJ mol(-1))/RT) Through comparison to the self-diffusion of Ti-44 in rutile TiO2, Nb-93 is interpreted to diffuse via the interstitialcy mechanism. The obtained tracer diffusion data are useful for ensuring compositional control during the processing of Nb-doped TiO2-based semiconductors using solid-state reactions between Nb2O5 and TiO2.