Cross sections for the 66Zn(n,p)66Cu reaction have been measured in the 4.2- to 10-MeV energy range using conventional activation techniques. This work provides results for an energy region where no other data are available. These results, and values from the literature for energies above 13 MeV, are used to provide an estimation of the cross-section excitation function from ∼4.2 to 20 MeV. An extrapolation of the cross section from 4.2 MeV to the effective threshold at ∼3 MeV is derived from calculations based on a semiempirical model that is fitted to the experimental data at higher energies. This excitation function is used to compute fission-spectrum-average cross sections, which are compared with corresponding values from the literature.