Si nanowires with different diameters are grown on catalyst coated Si substrates via a solid-liquid-solid mechanism. It is found that the thickness and type of catalyst film can modify the average diameter of Si nanowires obviously. The nanowires prepared on substrates deposited with Ni film of 40, 10, and 4nm thick have a mean diameter around 41, 36, and 24nm, respectively. Si nanowires with the smallest average diameter (～ 16 nm) are grown with a gold catalyst. Studies of diameter distributions show that the minimum diameter of nanowires does not shift with the average diameters spontaneously and has the same size of 10nm.