The impacts of different concentrations of bulk and nanosized TiO₂ on seed germination and seedling growth of wheat were studied in a randomized completely design with four replications in the College of Agriculture, Ferdowsi University of Mashhad, Iran, in 2011. The experimental treatments included five concentrations of bulk (1, 2, 10, 100, and 500 ppm), five concentrations of nanosized TiO₂ (1, 2, 10, 100, and 500 ppm), and control (without any TiO₂). Results indicated that among the wheat germination indices, only mean germination time was affected by treatments. The lowest and the highest mean germination time (0.89 vs. 1.35 days) were obtained in 10 ppm concentration of nanosized TiO₂ and control treatments, respectively. In addition, shoot length, seedling length, and root dry matters were affected by bulk and nanosized TiO₂ concentrations, significantly. Shoot and seedling lengths at 2 and 10 ppm concentrations of nanosized TiO₂ were higher than those of the untreated control and bulk TiO₂ at 2 and 10 ppm concentrations. Employing nanosized TiO₂ in suitable concentration could promote the seed germination of wheat in comparison to bulk TiO₂ but in high concentrations had inhibitory or any effect on wheat.