Size control of silicon nanowires (SiNWs) synthesized by laser ablation of a Si target with iron or nickel as catalysts were investigated by changing the synthesis parameters such as the content of catalyst in targets and laser power during synthesis. The diameter and length of SiNWs significantly depended on the synthesis parameters, i.e. the size of SiNWs can be controlled by the synthesis parameters. Manipulation of SiNWs was also performed during the observation of scanning electron microscope. By changing the degree of charge-up for free-standing adjacent intertwined SiNWs at an edge of Si substrate, the distance and speed of opening motion of them can be controlled. This motion is probably caused by the Coulomb repulsive interaction between them.