This study was carried out using a combination of PES and LEED techniques in one instrument. Both Cu(100) and Cu(111) surfaces did not show high tendency to adsorb N2O at room temperature. Dissociative adsorption was found to occur on the two surfaces N2O(ads) ?N2(g) + O?-(ads). Three surface structures were developed on Cu(100) ; (?2 x ?2)R45°-O at room temperature ; (?2 x 2?2)R45°-O after heating the crystal at 800 K in N2O and a complex structure denoted as (?2 x a) R45°-O, where a is not integrally related to copper lattice parameter, as a result of the interaction with thermally dissociated N2O. N2O adsorption on Cu(111) surface at room temperature did not change the primitive (1x1) structure of Cu(111) surface. N2O was molecularly adsorbed at 77 K. The adsorbed molecules were dissociated as a consequence of leaving the adsorbed phase in vacuum or during warming from 77 K to room temperature.