Structure of the excited states in9Be and10Be have been theoretically explored by means of the &agr;+&agr;+nand &agr;+&agr;+n+nmicroscopic cluster model respectively. Resonance excited states in9Be and10Be are localized by solving the two‐body scattering problems of {8Be(0+, 2+, 4+)+n,5He(3/2−, 1/2−)+&agr;} and {9Be(3/2−, 1/2+, 5/2−)+n,6He(0+, 2+)+&agr;} respectively. Our models have reproduced satisfactorily the experimental low‐energy spectrum in9Be and given various resonance excited states in10Be. Our model shows that the two and three competing configurations are quite essential to reproduce the anomalous 1/2+state in9Be and the second 0+state in10Be respectively. One of these configurations has a strong core(8Be) distortion which is induced by the valence neutron and is responsible for lowering thes1/2orbit in these states. Another configuration produces a spatially extended neutron distribution outside the core like the neutron halo. © 2004 American Institute of Physics