The characteristics of morphology and crystal structure of alpha-Al-12(Fe,Mn)(3) Si phase in two Al-Mn-Mg alloys in as-cast and homogenized states have been studied. The results show that the morphology of primary alpha-particles is the same as that of primary beta-particles in as-cast ingots and 'Al-spots' is only the characteristic of alpha-phase transformed from beta-phase. alpha-precipitates are sterically irregular plates. The alpha-phase precipitated from solid solution and transformed from beta-phase has an ordered body-centered cubic crystal structure. There is no obvious difference in the morphology of alpha-phase between two Al-Mn-Mg alloys. But in the alloy with high Si content there are more Mg2Si needles, which then cause the alpha-precipitates in alignment along the direction [1 0 0] of Al matrix during heating at lower temperature.