This study investigated the microstructure and mechanical properties of a wide-gap region brazed with various powders mixing ratios of additive powder to filler metal powder. The IN738 and BNi-3 alloy powders were used as additive and filler metal powder for the brazing process. The wide-gap brazing process was carried out in a vacuum of 2×10-5 torr. It was observed that the region brazed with only filler metal had a microstructure consisting of fully eutectic and dendrite structures. However, the region brazed with 60wt.% IN738 additive powder consisted of IN738 additive, Ni3B-Ni eutectic and (Cr, W)B. The fracture strength of the wide-gap region (70 wt.% additive and 30 wt.% filler metal powder) was as high as 687 MPa at room temperature. The Cracks in the wide-gap brazed region initiated at the Ni3B-Ni eutectic and (Cr, W)B, and then propagated through them. It was found that the Ni3B-Ni eutectic and (Cr, W)B in the brazed region are important microstructural factors affecting the mechanical properties of the wide-gap brazed region.