A method of fabricating fin structure is provided. A patterned catalyst layer and a patterned passivation layer extending along a first direction are formed on a substrate. The patterned passivation layer is located on the patterned catalyst layer. A carbon layer is formed on at least one side of the patterned catalyst layer and includes hollow carbon tubes arranged along the first direction. Each hollow carbon tube extends along a second direction. A removal process is performed to remove the top and a portion of the bottom of each hollow carbon tube closest to the substrate, so that remnants are left and serve as a mask layer. Two adjacent remnants form a stripe pattern extending along the second direction. The patterned passivation layer and the patterned catalyst layer are removed. The pattern of the mask layer is transferred to the substrate to form fin structures. The mask layer is removed.