The negative parity high spin states of even-odd Er nucleus with mass number 159 ≤ A ≤ 165 were studied within the framework of the interacting boson-fermion model. The single fermion is assumed to be in one of the lh9/2, 3p3/2, 2f5/2 and 3p1/2, single particle orbits. It was found that the energy spectra up to I=57/2^- of the even-odd Er isotopes could be reproduced quite well. The observed B (E2) values were calculated and compared with the experimental data.