A hydrophobic surface has been fabricated on aluminum by two-step surface treatment processes consisting of structure modification and surface coating. Nature inspired micro · nano scale structures were artificially created on the aluminum surface by a blasting and Ar ion beam etching. And a hydrophobic thin film was coated by a trimethylsilane ((CH3)3SiH) plasma deposition to minimize the surface energy of the micro · nano structure surface. The contact angle of micro · nano structured aluminum surface with the trimethylsilane coating was 123o (surface energy: 9.05 mJ/m2), but the contact angle of only trimethylsilane coated sample without the micro · nano surface structure was 92o (surface energy: 99.15 mJ/m2). In the hydrophobic treatment of aluminum surface, a trimethylsilane coated sample having the micro · nano structure was more effective than only trimethylsilane coated sample without the micro · nano structure.