Electronic excitation spectrum of thiophene was investigated by the symmetry-adapted cluster (SAC)/SAC configuration interaction method. Seventy singlet and four lowest triplet electronic states of thiophene were computed to give a detailed satisfactory theoretical interpretation of the vacuum ultraviolet (VUV) spectrum and the electron energy loss spectrum of thiophene. The present calculations gave the 2 (1)A(1) valence state at 5.41 eV and the 1 B-1(2) valence state at 5.72 eV with oscillator strengths 0.0911 and 0.1131, respectively, and the 5 (1)A(1) valence state at 7.32 eV and the 4 B-1(2) valence state at 7.40 eV with oscillator strengths 0.3614 and 0.1204, respectively. These valence-excited states were assigned to the two strong absorption bands of the VUV spectrum centered around 5.5 and 7.05 eV, respectively. A number of Rydberg transitions were obtained and assigned to the 6.0, 6.6, and 7.5-8.7 eV, etc. energy regions. The similarities and differences in the electronic excitations between thiophene and other five-membered ring compounds were discussed. The accuracy and assignment of the present results are compared with those of the recent theoretical studies by CASPT2 and multireference double configuration interaction methods.