Mechanical properties of a high packing ratio MgB 2 bulk sample processed by spark plasma sintering (SPS) were evaluated at 77 K through bending tests for specimens cut from the bulk sample. The effects of the packing ratio and temperature on the fracture strength of MgB 2 bulk are discussed. The fracture strength at 77 K of the MgB 2 bulk processed by SPS was higher than that at room temperature. The packing ratio of the MgB 2 bulk processed by SPS was higher than those of other MgB 2 bulks processed by sintering under the ambient pressure and hot isostatic pressing. The fracture strength was improved by increasing the packing ratio. The fracture strength at a very low temperature was estimated from the bending test results at 77 K and room temperature. The fracture strength at 20 K of the MgB 2 bulk processed by SPS was estimated to be around 425 MPa. © 2015 IEEE.