Room temperature deposition of Al on Si(1 1 1) root3 x root3-Al surface shows two-dimensional growth mode and results in an excellent epitaxial film of Al(1 1 1). Especially, in the initial growth stage, a transient behavior is observed in the RHEED intensity oscillation curve of the specular beam. By means of dynamical analysis of the RHEED rocking curves, the transient surface structure has been clarified as entirely filled T-4 Site (EFT) structure, where deposited 2/3 monolayer Al atoms sit on the residual 2/3 monolayer T-4 sites and the height is slightly lower than that of initially situated 1/3 monolayer Al atoms at T-4 sites of Si(1 1 1) root3 x root3-Al structure. The EFT surface structure is considered to play an important part leading to the excellent epitaxial growth Of Al(1 1 1).