The intermetallics of (Mo1-xNbx) Si-2 consisted of C11(b) phase and C40 phase when x is equal to 0.05, 0.10 and 0.15, and consisted of only C40 phase when x is equal to 0.20. Systemic heat treatments were conducted on the alloys. The evolution of microstructure was investigated with varying annealing temperature and time. Through the appropriate heat-treated processing, the microstructures of the alloys can be controlled to form full lamellar structure.