The microstructure and tensile properties of twin-roll cast (TRC) Mg–6% Zn–1% Mn (ZM61) alloys with varying Al contents were investigated. The microstructure of the alloys becomes finer with the addition of Al. The type of dispersoid particles also changes with the Al addition: from MgZn2 in ZM61 alloy to Al8Mn5 in the ZM61–1% Al (ZMA611) and ZM61–3% Al (ZMA613) alloys. ZMA611 alloy has a better combination of tensile properties than ZM61 alloy. However, ZMA613 alloy shows poor ductility due to the formation of coarse Mg21(Al, Zn)17 phase during TRC.