Recently, the use of stainless steels have been increased steadily as a sustainable structural material in infrastructures and thanks to its superior corrosion resistance, fire resistance and ductility compared with those of carbon steels. In this paper, block shear fracture behaviors in base metal of fillet-welded connection fabricated with austenitic stainless steel (STS304L) were investigated through monotonic tensile test. Main variables are weld lengths in the longitudinal and the transverse directions of applied force. Gas tungsten arc welding (GTAW) which is also known as tungsten inert gas (TIG) welding was chosen to join two metals. As a result, test specimens failed by typical block shear fracture (the combination of tensile fracture and shear-out fracture) in base steel. With the increase of two weld lengths, the ultimate strengths of specimens tended to get higher. Block shear fracture strengths predicted by current design specifications and existing proposed equations for welded connections were compared with those of test results. It is found that the discrepancy of strength prediction resulted from the effect of stress triaxiality on welded connections and the difference of material properties with carbon steel. Therefore, modified block shear fracture equation was suggested in this paper.