The s-cis and s-trans isomer radical cations of hexafluoro-1,3-butadiene (s-cis-HFBD+ and s-trans-HFBD+) were generated by a gamma-irradiated solid solution of the neutral HFBD molecule in solid matrix at 77 K and observed by means of electron spin resonance (ESR) and electronic spectroscopies. In comparing the experimental isotropic and anisotropic F-19 hyperfine splittings with the computational ones by the DFT B3LYP and MP2 methods, the generated s-cis-HFBD+ and s-trans-HFBD+ radical cations were confirmed to be (2)A(2) and B-2(g) electronic ground states in C-2v and C-2h symmetries, respectively. The present spectroscopic study revealed that the relative abundance of s-cis-HFBD+ to s-trans-HFBD+ was 4.0 immediately after being formed by gamma-irradiation, and subsequently most s-cis-HFBD+ was isomerized to s-trans-HFBD+ by visible-light illumination with 500-600 nm wavelength. The process of nonplanar HFBD ionizing to form stable planar s-cis- and s-trans-HFBD+ and the reaction mechanism of the cis-to-trans photoisomerization were discussed by (MS-)CASPT2//CASSCF calculated vertical excitation energies (T-v) and torsional potential energy curves (TPECs) of HFBD and HFBD+.