Fully-reversed total-strain-amplitude-controlled fatigue tests were performed in laboratory air at room temperature for the magnesium alloy AZ91. Experimental results showed that during the experiment significant cyclic strain hardening occurred throughout the imposed strain amplitudes. It was found that the relationship between plastic strain amplitude, elastic strain amplitude and reversals to failure can be well described by Basquin and Coffin-Manson equations. In addition, the strain fatigue parameters of the AZ91 alloy were determined through analyzing the corresponding strain fatigue life data.