As-cast AZ80 magnesium alloy consists of α-Mg, eutectic product of α-Mg and γ-Mg17Al12, with the latter present in the form of partially and fully divorce eutectic. There occurs dissolution of harder γ-Mg17Al12 phase during homogenization treatment at 400 ° and 439 °C. The proportion of the α-Mg and γ-Mg17Al12 phase was varied by solutionizing the alloy for various lengths of time at these temperatures, in order to investigate the kinetics of phase transformation and to evaluate the effect of phase proportion, size and morphology on room temperature tensile properties. It was found that the yield strength decreases with the increase in solutionizing temperature from 400° to 439 °C and at the same time, ductility in general increases with the increasing solutionizing temperature. The variation in tensile properties and the nature of fractographs were analyzed in terms of the effects of microstructure. © (2014) Trans Tech Publications, Switzerland.