The low cyle fatigue (LCF) behavior of an extruded AZ31B magnesium alloy with the fiber texture components was investigated under asymmetric loading at different total amplitudes. It was found that the alloy exhibits cyclic strain-hardening characteristic at the strain amplitudes ranging from 0.7% to 1.5%, however, the stress amplitude versus the number of reversals becomes almost constant as the strain amplitude reaches up to 2.0%. The cyclic hardening dominantly originates from tensile deformation when strain amplitude is below 1.5%, and its rate increases with the increment of strain amplitude; the hysteresis loop becomes asymmetrical in shape when the strain amplitude increases. From the deformed microstructures, it suggests that the cyclic plastic deformation at the low strain amplitudes is mainly associated with the dislocation slips while the twinning-detwinning is the dominant deformation way at high amplitudes. The asymmetry of the LCF behavior is discussed in terms of the difference of the plastic deformation mechanisms between compression and tension in cyclic reversals.