Samples of Dy166 were produced by successive neutron capture in stable Dy164. This isotope decays by beta-ray emission with an 80.2-hr half-life to states in Ho166. This isotopic assignment of previous authors is confirmed. Separations of the parent and daughter activities were carried out by use of an ion-exchange column. Scintillation studies were made with a 256-channel scintillation coincidence spectrometer. Internalconversion electrons were measured in magnetic spectrographs with permanent magnets and the continuous beta spectra were observed with a 180° magnetic spectrometer with a variable field. The seven gamma-ray transitions observed had energies of 28.1, 54.2, 82.5, 288, 344, 375, and 428 kev. Beta-ray branches of 481 and 402 kev were observed with the magnetic spectrometer; two others of 114 and 56 kev are postulated for the decay scheme. The decay scheme presented indicates the existence of five levels in 67Ho166 at 0(0-), 54(2-), 82(1-), 370, and 428(1+) kev. The ground state and first two excited states are interpreted as members of a rotational band with K=0. This interpretation implies that in odd-odd nuclei the level sequence can be inverted for the first two excited states of such a band.