The dry chemical method is developed to fabricate CuO nanostructures via microwave assisted irradiation in ionic liquid 1-butyl-3-ethyl imidazolium tetrafluoroborate ([BMIM][BF4]). Both nanoparticles (20 nm in size) and nanorods (10-20 nm in diameter and 100-200 nm in length) of monoclinic CuO were obtained. The as samples were characterized by FTIR, XRD, TEM, SADE. The morphologies of the nanostructures can be controlled by the amount-tuning of NaOH and ionic liquids. The growth mechanism of CuO nanostructures is investigated.