The fatigue behaviors of mechanically alloyed Al-4Mg alloys dispersed with either Al₂O₃, or MgAl₂O₄, oxide particles were investigated. This study maily concerned with the role of coherency of dispersed particles with the matrix on the fatigue behavior of the alloys. The MgAl₂O₄, which has a spinel structure with the lattice parameter of exactly the twice of A1 showed the habit relation with the matrix. The mechanically alloyed Al-4Mg alloys showed stable stress responses with fatigue cycles from start to failure regardless of strain amplitudes and of existence of dispersoids. The Al-4Mg alloy dispersed with MgAl₂O₄O₄showed not only the better static mechanical properties but also the better low cycle fatigue resistance than that with Al₂O₃, i.e., much higher plastic strain energy dissipated to failure, at low strain amplitude. However, this alloy showed inferior fatigue resistance to that dispersed with Al₂O₃or that without dispersion at high strain amplitude. These results imply that MgAl₂O₄may promote lowering the stacking fault energy of the alloy inherited from the coherency with the matrix so that dislocations shuttle back and forth on the same slip plane without cross slipping to other planes during fatigue at low strain amplitude resulting in long fatigue life.