Distinct site- and state-selective dissociation following the O1s core-excitation has been found in the gaseous molecules of methyl trifluoroacetate (MTFA). The site- and state-selective dissociation was examined by measuring the branching ratios of dominant CH₃⁺ and CHO⁺ fragments. The branching ratios from MTFA showed that site-selective dissociation takes place via the excitation from the different atomic sites to the same π^*_CO resonance state, (O1s_CO^-1π^*_CO) and (O1s_OMe^-1π^*_CO). A pronounced O1s_OMe site-selectivity was identified by a significant increment of CHO⁺ formation at the (O1s_OMe→π^*_CO) band. The site-selectivity was also justified by an equivalent core approximation using the density functional theory calculation. State-selective dissociation was identified among the (O1s_OMe^-1π^*_CO), (O1s_OMe^-1σ^*_O-Me) and (O1s_OMe^-1σ^*_C-OMe) transitions originated from the same OMe core. State-selective production of CH₃⁺ could be found at the (O1s_OMe→σ^*_O-Me) band, whereas state-selective formation of CHO⁺ was observed at the (O1s_OMe→π^*_CO) and (O1s_OMe→σ^*_C-OMe) bands.