Experimental evidence shows that small Cu(2)O nanoparticles exhibit ferromagnetic or paramagnetic properties, allowing for the promising possibility to recycle the catalyst Cu(2)O easily in wastewater treatment. In this paper, theoretical calculation studying the magnetic property of copper/oxide clusters is reported. A series of Cu(m)O(n) ((m, n) = (4, 1); (4, 2); (4, 5); (16, 15); (28, 15); (44, 15); (28, 27)) clusters were investigated using generalized gradient approximation (GGA) and the Hubbard U (GGA+U) method within density functional theory (DFT). It is found that the electronic structures of bulk Cu(2)O calculated by the GGA and GGA+U are similar. The structures of Cu(m)O(n) ((m, n) = (4, 1); (4, 2); (4, 5)) are all planar. For the bulk-product Cu(m)O(n) ((m, n) = (16, 15); (28, 15); (44, 15); (28, 27)), O atoms prefer to be the outermost atoms. We classified two types of clusters on the basis of their O to Cu atomic ratios. One is O-rich clusters, i.e., Cu(4)O(5), Cu(16)O(15), and Cu(28)O(27). The other is O-poor clusters, i.e., Cu(4)O, Cu(4)O(2), Cu(28)O(15), and Cu(44)O(15). The calculation results show that the O-rich clusters have longer average Cu-Cu bonds and larger binding energy than those of the O-poor ones. More interestingly, the former are magnetic and give ferromagnetic ordering while the latter are nonmagnetic. The hydrogenation of O-terminated clusters can improve its stability but suppress its magnetism. The study may be extremely useful for the potential applications of Cu(2)O nanoparticles in the catalysis and semiconductor fields.