A microelectrochemical technique was applied to ascertain the pit initiation behavior at the δ/γ-grain boundary of Type 304L austenitic cast stainless steel in 1 M NaCl solution. The size of electrode area was changed from ca. 0.01 mm2 (100 μm×100 μm) to ca. 100 mm2 (10 mm×10 mm). The density for pit initiation site of Type 304L cast stainless steel was estimated to be around 1 site/mm2. From anodic polarization, transmission electron microscopy, and energy-dispersive X-ray fluorescence analysis, P-and S-segregation was confirmed to be associated with the pit initiation at δ/γ-grain boundary. In addition to this, Si-segregation or Si-containing inclusion at the boundaries was thought to be a factor affecting the pit initiation at the δ/γ-grain boundary.