One dimensional structures with nanometer diameters, such as Si nanowires, have great potential for understanding and testing fundamental concepts about the roles of dimensionality in optical, electrical and mechanical properties and for applications ranging from nanoelectronics to biosensing. Here we successfully grow high aspect ratio Si nanowires using Ni catalyst. At high temperature, we found that Ni catalyst layer changed to irregular starfish like structure. Detailed microscopy results showed that catalyst particle size has no relation with the diameter of Si nanowires. Most Si wires grow from the irregular catalyst tentacles. Furthermore, to understand how catalyst size and shape affect Si wires formation, we use EB writer and lift-off process to make various types of Ni nano catalyst corners.