A study of valence electronic properties of S-ethyl chlorothioformate (S-ethyl chloromethanethioate), CIC(O) SCH2CH3, using HeI photoelectron spectra (PES) and synchrotron radiation is presented. Moreover, the photon impact excitation and dissociation dynamics of CIC(O)SCH2CH3 excited at the S 2p and Cl 2p levels are elucidated by analyzing the total ion yield (TIY) spectra and time-of-flight mass spectra acquired in multicoincidence mode [photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO)]. The HeI photoelectron spectrum is dominated by features associated with lone-pair electrons from the CIC(O)S-group, the HOMO at 9.84 eV being assigned to the n(pi)(S) sulfur lone-pair orbital. Whereas the formation of C2H5+ ion dominates the fragmentation in the valence energy region, the most abundant ion formed in both the S and Cl 2p energy ranges is C2H3+. Comparison with related XC(O)SR (X = H, F, Cl and R= -CH3, -C2H5) species reveals the impact of the alkyl chain on the photodissociation behavior of S-alkyl (halo)thioformates.