Samples of YBa2(Cu0.85Sn0.15)3O7−y (1-2-3), La2(Cu0.95Sn0.05)O44−x, and La1.85Ba0.15(Cu0.95Sn0.05)O4−x (2-1-4), with different oxygen stoichiometry, have been studied by Mossbauer spectroscopy. These measurements reveal the existence of two inequivalent sites for Sn in the (1-2-3) compounds. The (1-2-3) spectra display two quadrupole doublets which we associate with Sn in Cu(1) and Cu(2) sites, respectively. La compounds show a single quadrupole doublet.