Nucleation and growth properties of Si1-xGex (0≦x≦0.3) have been investigated by using ellipsometric spectroscopy. The incubation time and the crystallization time significantly decrease with increasing x; the estimated incubation time (and crystallization time) in Si0.7Ge0.3 is about 1/100 of that in Si. During the incubation time, the increase of the crystallinity has been observed which corresponds to the nucleation of crystal seeds. From the behavior of the crystallinity during the incubation and the crystallization time, we estimated the activation energy of the nucleation and the crystallization. Both energies monotonically decrease with increasing x. The saturated crystallinity after crystallization decreases with increasing x. It has been found that the effect of Ge reduces the crystallinity of Si1-xGex while significantly enhancing the crystallization.