Vibrational spectra of trans- and cis-1-C3H5Br cations in the ground electronic states were obtained by the one-photon mass-analyzed threshold ionization (MATT) spectroscopy using the coherent vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. From the MATT spectra, ionization energies of trans- and cis-1-C3H5Br to the ionic ground states have been determined to be 9.2693 +/- 0.0006 and 9.3140 +/- 0.0006 eV, respectively. Almost complete vibrational assignments for the peaks in the MATT spectra were possible by utilizing vibrational frequencies and Franck-Condon factors calculated at the B3LYP and BP86 levels with the 6-311++G(3df,3pd) basis set.