The creep behavior of the DZ125 superalloy at high temperatures has been investigated based on the creep properties measurement and microstructure observations. The experimental results show that, after full heat treatment, the fine and coarser cuboidal γ′ precipitates distributed in the dendrite arm and inter-dendrite regions, respectively, the boundaries with various configurations located in the inter-dendrite regions. In the primary creep stage, the cuboidal γ′ phase in the alloy transformed into the rafted structure along the direction vertical to the stress axis. The dislocations slipping and climbing over the rafted γ′ phase are attributed the deformation mechanism of the alloy during steady-state creep. The (1/2)〈1 1 0〉 dislocations slipping in the γ matrix and 〈1 1 0〉 super-dislocations shearing into the γ′ phase are the deformation mechanisms of the alloy in the latter stage of creep. And then the alternate slipping of dislocations results in the initiation and propagation of the micro-cracks along the boundaries until the occurrence of the creep fracture. Since the grain boundaries with various angles relative to the stress axis distribute in the different regions, the initiation and propagation of micro-cracks along the boundaries display the various features.