A first-principles total-energy plane-wave pseudopotential method based on density functional theory has been used to investigate the site preference of Si in Al(3)Ti. The site preference parameter S has been calculated and the value of S decreases on increasing Si concentration, but is always greater than 1 while the Si concentration is lower than 25 at.%, indicating Si has a strong site preference for the Al sublattice. The physical origin of the site preference of Si in Al(3)Ti was studied by calculating the densities of states (DOSs) of the Al(3)Ti-Si systems. The heat of formation and the DOS of the position of the Fermi energy level were also studied to analyze the site preference of Si in Al(3)Ti.