Mg-9Al-xRE magnesium alloys were studied, where x is 0, 0.4, 0.8, 1.2 and 1.6% (inweight percent, wt%), respectively. Influence of rare earths (RE) on microstructureand strength in both T4 (solute heat treatment) and T6 (solute heat treatment andartificial ageing treatment) were investigated. Strength of specimen was tested at am-bient temperature. The microstructure was analyzed by optical microscopy, scanningelectron microscopy (SEM) and X-ray diffraction analysis. RE additions improvedT4 tensile strength of the treated alloys. Small addition (0.4wt%) of RE greatly im-proved the strength of ageing treated (T6) Mg-9Al alloy, but further additions caused decreasing.