This study describes fracture strength ofelectro-slag welded (ESW) connections under biaxial loading condition. The discussions are based on model test results of ESW joints and finite element analysis (FEA) results with corresponding analytical models. Case studies are also made where an axial force ratio and a penetration shape are the analytical parameters. Results are summarized as follows; 1) The model test results show roughly positive correlation between the fracture toughness and the fracture strengths of ESW joints; 2) The model test results and the corresponding FEA results correlate the fracture toughness with calculated equivalent maximum principal stress (MPA); 3) In the results of the case studies, the calculated MPA in a heat affected zone highly depends on an ESW fusion line position.