This study examined the degradation of perfluorooctanesulfonate (PFOS) in electrochemical oxidation (EO) processes in the presence of trichloroethylene (TCE). The EO experiment was performed in a gas-tight reactor using Magnéli phase titanium suboxide (Ti4O7) as the anode. The experimental data demonstrated that 75% of PFOS (2 μM) was degraded at 10 mA/cm2 current density in 30 min without TCE present in the solution, while the presence of 76 μM TCE apparently inhibited the degradation of PFOS, reducing its removal down to 53%. Defluorination ratio suggested that PFOS was significantly mineralized upon EO treatment, and it appeared to be not influenced by the presence of TCE. The respective pseudo-first order rate constants (kobs) of PFOS removal were 0.0471 and 0.0254 min-1 in the absence and presence of TCE. The degradation rates of both PFOS and TCE increased with current density rising from 2.5 to 20 mA/cm2. In the presence of TCE, chloride, chlorate, and perchlorate were formed that accounted for 79.7 %, 5.53%, and 1.51% of the total chlorine at 60 min. This work illustrates the promise of the Magnéli phase Ti4O7 electrode based electrochemical oxidation technology for degrading per- and polyfluoroalkyl substances (PFASs) and co-contaminants in groundwaters.