Irradiation-Assisted Stress Corrosion Cracking (IASCC) is a material degradation phenomenon observed in austenitic stainless steels Pressurized Water Reactor (PWR) internal structures, leading to the initiation and propagation of InterGranular (IG) cracks. Grain boundary (GB) fracture properties are expected to play a key role for the predictive modelling of initiation. However, experimental data for austenitic stainless steels remain scarce. Therefore, an experimental protocol is built to assess the oxidized grain boundary fracture properties of a FeCr12Ni26Si3 austenitic stainless steel. Prior to tests, the material has been exposed to PWR nominal environment for 3680h and 7470h, leading to the formation of a duplex oxide layer and micron-scale oxide penetration along some GBs. Oxide penetration depth at the grain boundaries in the 7470h oxidized sample appeared to be higher than in the 3680h sample. After Electron BackScatter Diffraction (EBSD) mapping to identify grain boundaries, micro-cantilevers containing a single grain boundary have been milled using Focused Ion Beam (FIB) and tested through in-situ micro-bending tests at room temperature inside a Scanning Electron Microscope (SEM). Intergranular cracking has been observed on 12 micro-cantilevers, either inside the GB oxide or at the interfaces between the oxide and the metal. Fracture energy has been evaluated based on energy balance, leading to values comprised between 2J/m2 to 22J/m2. In addition, beam theory has been applied in order to determine the stresses at the crack initiation point, ranging from 338MPa to 857MPa. The scatter associated with both fracture energy and critical stress is discussed.