The microstructure and corrosion behavior of the as-cast hot-dip Zn-5Al-xMn (x=0，0.1，0.2，0.3) alloys have been investigated by SEM, EDS, electrochemical test techniques, etc. The results indicate that a small addition of Mn in as-cast Zn-5Al alloy can greatly inhibit the formation of primary β-Zn phase. When the Mn addition is 0.2% (in mass), the amount of β-Zn phase is the least and the percentage of eutectic composition reaches the maximum. The corrosion potential of the tested alloy moves positive direction, while the corrosion current density decreases first and then increases as increasing of Mn addition. The corrosion current density of the Zn-5Al-0.2Mn alloy has the minimum value of 1.403 μA/cm², with which the impedance spectra at both high and low frequencies reach the maximum. The primary β-Zn phase is corroded preferentially in Zn-5Al alloy, but uniform corrosion happens in Zn-5Al-0.2Mn alloy for little amount of β-Zn phase. The corrosion products of Zn-5Al-0.2Mn is the most compact in the Zn-5Al-xMn alloys.