The power characteristics of the Mg-Air fuel cell were investigated with regard to variation of load conditions. The types of load current using for the Mg-Air fuel cell with 10% NaCl electrolyte were step type, ramp type and pulse type. It was found that transient phenomena occurred in the step current load, which is due to activate of the oxidation-reduction reaction process. And the transient time increase with the load current increase. In the load current of ramp type, the slop of voltage drop increased with current load slop ${alpha}$ increase. The load voltage and power decreased according to the pulse period of load current decrease were attributed to the metal sludges.