The spectrum of the kryptonlike ion Nb vi was observed from 325 to 2700 Å with sliding-spark discharges on 10.7-m normal-incidence and grazing-incidence spectrographs. Experimental energies were determined for all levels of the 4s24p6, 4s24p5 4d, 4f, 5s, 5p, 5d, 5g, 6s, and 4s4p64d configurations as well as for some levels of the 4s24p56g and 6h configurations. A total of 303 lines are now classified as transitions between 99 observed levels. Large hyperfine splittings were found for several levels of the 4p55s and 5p configurations. The observed configurations were theoretically interpreted by means of Hartree–Fock calculations and least-squares fits of the energy parameters to the observed levels. An improved value of the ionization energy was determined from the 4p55g, 6g, and 6h configurations. The adopted value of the limit is 823 240 ± 50 cm−1 (102.069 ± 0.006 eV).