Provided is a method of forming fine patterns capable of minimizing LER and LWR to form high quality nanopatterns, by using a block copolymer having excellent etching selectivity. Provided is the block copolymer comprising a first block having a repeating unit represented by a following chemical formula 1, and a second block having a repeating unit represented by a following chemical formula 2, wherein R1-R5, X1-X5, 1, n and m are as defined by claim 1.