Hyperfine structure spectra of singly ionized lanthanum and praseodymium have been measured by collinearfast-ion-beam laser spectroscopy. All the spectral lines were resolved and the magnetic dipole and electric quadruplecoupling constants of the metastable levels and excited levels were determined. Our results are in agreement withthe published data within the experimental uncertainty. For praseodymium ions, the accuracy of the magnetic dipolecoupling constants are improved by one order of magnitude compared with other published data, and the electricquadruple coupling constants are reported for the first time.