The creep behavior of the Ir-Nb alloy with cuboidal L 12 precipitates in a fcc phase and the Ir-Zr alloy with a lamellar structure consisting of the fcc and L1(2) phases was investigated at temperatures between 1773 and 2073 K. The stress exponent and the activation energy of the Ir-based binary alloys were estimated from the creep curves. The deformation mechanism is discussed in terms of the deformation structure observed in transmission electron microscopy, the stress exponent, and the activation energy.