Due to the low density, high specific strength and stiffness, magnesium alloys are being considered for automotive and aerospace applications. The structural applications of magnesium components need a decent low--cycle fatigue performance, because cyclic loading is often encountered. In order to identify the low--cycle fatigue behavior of the newly developed Mg--x%Al--3%Ni(x=4, 5, 6, 7, mass fraction) extruded magnesium alloys with different contents of Al, the total strain--controlled low--cycle fatigue tests were performed at room temperature. The cyclic stress response, strain fatigue life and cyclic stress--strain behaviors were investigated for the hot--extruded Mg--x%Al--3%Ni alloys. The results of the low--cyclic fatigue tests show that the hot--extruded Mg--x%Al--3%Ni alloys exhibit the cyclic strain hardening during fatigue deformation. The dependences of the strain fatigue life on plastic strain amplitude and elastic strain amplitude can be described by the Coffin--Manson and Basquin equations, respectively. In the hot extruded Mg--x%Al--3%Ni alloys with different contents of Al, the extruded Mg--5%Al--3%Ni alloy gives the longest fatigue life and the highest fatigue resistance. In addition, a linear relation between the cyclic stress amplitude and cyclic strain amplitude can be noted for the hot--extruded Mg--x%Al--3%Ni alloys.