The electron-capture decay 165Tm → 165Er has been investigated with the six-gap β-ray spectrometer as well as Ge(Li) and NaI(Tl) γ-ray detectors. The single γ-ray spectrum, e-γ and γ-γ coincidence spectra have been studied. Some tentative levels have been confirmed and several new established. The structure of the non-rotational states in 165Er is discussed in terms of a model in which the interaction of quasi-particles with quadrupole and octupole phonons is considered. The energy spacing between states with a predominant single-particle character is compared with the energy spacing calculated on the basis of the pairing force theory. © 1968.