[en] We report the effect of Nb doping on the upper critical field of the cubic Laves-phase superconductor HfV₂ studied in a series of HfV_2−xNb_x samples with 0 ≤ x ≤ 0.3 under pulsed fields up to 30 T. The undoped HfV₂ undergoes a martensitic structural transition around 110 K, and becomes superconducting below T _c = 9.4 K. Upon Nb doping, while the structural transition is suppressed for x ≥ 0.1, a maximum in T _c of 10.1 K and zero-temperature upper critical field B _c2(0) of 22.4 T is found at x = 0.2, which is ascribed to an increase of the density of states at the Fermi level. For all samples, the temperature dependence of B _c2 can be well described by the Werthamer–Helfand–Hohenberg theory that takes into account both the spin paramagnetic effect and spin orbit scattering. In addition, a comparison is made between the B _c2 behavior of HfV_2−xNb_x and those of Nb–Ti and Nb₃Sn. (paper)