The He I photoelectron spectra (PES) of HOClO3 and FOClO3 are reported. The assignments of the PES bands are made on the basis of band shapes, relative band intensities, and the results of ab initio calculations using GAUSSIAN 94 at the 6-31G* basis set level. The two peaks (at 12.37 and 12.77 eV) in the first PES band of HOClO3 are designated as electron ionizations from HOMO 8a "(25), SHOMO 7a "(24), and 17a＇(23) orbitals, respectively, and they can be attributed to a Jahn-Teller effect on the largely lone-pair orbitals of three oxygen atoms in the ClO3 atomic group of HOClO3. The absence of splitting in the first PES band of FOClO3 centered near 13.20 eV is attributed to a loss of C-3v, symmetry in the ClO3 atomic group of FOClO3. This band is assigned to electron ionizations of the HOMO 9a "(29), SHOMO 8a "(28), and 20a＇(27) orbitals, in which the three oxygen atoms of the ClO3 atomic group of the FOClO3 molecule hold dominant weight.