Study of plasmon-induced charge transfer mechanisms in gold-TiO₂ system is very significant in the solar cell application. Gold nanodots exhibit a broad interband in the UV region and a pronounced narrow surface plasmon band in the visible region originating from the collective oscillation of free conduction electrons. Under the plasmon band excitation (at 550 nm), photo-induced electron injection from gold to TiO₂ has been observed by our group using IR-probe femtosecond transient absorption spectroscopy. Transient absorption kinetics probed at 3440 nm were studied to observe intraband free electron adsorption in TiO₂. To further clarify plasmon induced charge transfer mechanism, TiO₂ particle size effect has been studied. In our experimental study, TiO₂ with different diameter (9, 20, 30, 50 nm) were loaded with 10 nm gold nanodots. We found that the electron injection times were within 240 fs and that the measured back electron transfer kinetics up to 1.5 ns were strongly dependent on the diameter of TiO₂. We explained different charge recombination kinetics by different diffusion distance of free electrons within TiO₂ particle and different contact area at the gold/TiO₂ interface. To compare the electron injection efficiency between plasmon band excitation and interband excitation, we changed the excitation wavelength from 400 nm to 600 nm that covered both interband and plasmon bands, and the electron injection efficiencies in gold/TiO₂ systems were investigated. The plasmon-induced mechanisms will be discussed in detail.