The nucleation and initial growth of titanium suicide on Si(111)7×7 surface has been studied using the scanning tunneling microscopy(STM) in ultrahigh vacuum. At room temperature Ti atoms react with Si atoms and preferentially adsorb on faulted half of the 7×7 surface. By annealing at 600°C, islandlike structures(amorphous titanium suicide) and striplike structures(crystalline titanium suicide) are formed. Annealing at 700°C drives the growth of striplike structures from islandlike structures. The striplike structures grow parallel to specific directions on the 7×7 surface.