Using Cr-Nb MA powders ball milled for 30 h then annealed for 3 h, the effects of annealing temperature on Laves phase Cr2Nb synthesizing by solid phase thermal reaction have been investigated. The lowest annealing temperature of the powder for full synthesizing of Laves phase Cr2Nb was obtained. The optimized low temperature annealing parameters for Laves phase Cr2Nb synthesizing by solid phase thermal reaction can theoretically provide guidance for preparing both high strength and high tough Cr2Nb alloy or Cr2Nb-based composite with micro- / nano-grains by a process of mechanical alloying followed by a hot pressing or sintering.