The microstructures of the alloys near the Al3Ti-8Mn composition region of the Al-Ti-Nb-8Mn quaternary system changewith variation of the Nb content. The microstructures have been investigated using optical microscopy, scanning electron microscopy(SEM) and transmission electron microscopy(TEM). It is determined that in Al67Mn8Ti22-based alloys modified with Nb the secondphases can be DO22 Al3 (Ti,Nb), L10 TiAl or Ga2Hf type of Al2Ti. The microstructures of four typical experimental alloys, A67,Mn8Ti23Nb2, Al59Mn8Ti30Nb3, Al65Mn8Ti26.5Nb0.5 and Al65Mn8Ti23Nb4,are presented in this paper. The second phase Al3 (Ti, Nb)particles con be dispersed blocky or dendritic,the L10 TiAl particles are ripple-like or needle-like, and Ll10 TiAl arrays alternately withL12 matrix. The netty Al2Ti phase is plate-like under TEM and distributes across the L13 matrix.