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The effect of Si-phase on tension-compression low cycle fatigue properties of Al-Si eutectic alloys was investigated. Fatigue test specimens were prepared from two materials produced by two processes, continuous-casting and extrusion. The results obtained are: (1) In the case of continuous-casting, all the fatigue fractures were caused by shear type crack initiation and propagation, resulting shorter fatigue life. (2) In the case of extrusion, the fatigue fracture origin was at Si-phase. (3) In both cases, continuous casting and extrusion, the crack initiation and growth mechanism were essentially identical with those of high cycle fatigue in the range Nf<107. (4) Manson's law can be applied only to the case (2) (extrusion) but not to the case (1) (continuous casting). This is because in the case (1) most of fatigue life is consumed by the growth process of small crack of mode I but in the case (2) crack grows by mode II.