In order to determine the influence of rare earth element Sc on the low-cycle fatigue behavior of casting Al-9.0%Si-4.0%Cu-0.4%Mg alloy with T6 treated state, the comparison in the low-cycle fatigue behavior was performed for the Al-9.0%Si-4.0%Cu-0.4%Mg and Al-9.0%Si-4.0%Cu-0.4%Mg-0.3%Sc alloys. The results show that at the low total strain amplitude, the Al-9.0%Si-4.0%Cu-0.4%Mg alloy exhibits the cyclic strain hardening during whole fatigue deformation, while the Al-9.0%Si-4.0%Cu-0.4%Mg(-0.3%Sc) alloy exhibits the cyclic strain hardening in the initial stage of fatigue deformation and then the stable cyclic stress response in the later stage of fatigue deformation. At the higher total strain amplitudes, the Al-9.0%Si-4.0%Cu-0.4%Mg(-0.3%Sc) alloys exhibit the cyclic strain hardening. The addition of Sc can effectively enhance the cyclic deformation resistance and prolong the fatigue lives of theAl-9.0%Si-4.0%Cu-0.4%Mg alloy with T6 treated state. At the lower total strain amplitudes, the cyclic deformation mechanism of the Al-9.0%Si-4.0%Cu-0.4%Mg(-0.3%Sc) alloys with T6 treated state is the plane slip, while at the higher total strain amplitudes, the cyclic deformation mechanism becomes the wavy slip.