A novel Mg-8Al-2Sn-1Zn alloy with a bimodal structure prepared by hard-pate-rolling (HPR) exhibits both higher tensile strength and ductility than its fine-grained counterparts prepared by conventional rolling. By delicate electron back-scatter diffraction (EBSD) analysis, we found fine grains with weak basal texture is beneficial for basal slip and favors initial deformation. Meanwhile, coarse grains with a strong basal texture could accommodate abundant newly generated dislocations, promoting work hardening after fine grains are saturated with dislocations. For the first time, individual roles of fine and coarse grains and their synergy effect on enhancing ductility in bimodal structured Mg alloys is clarified. Display omitted •A bimodal grain-structured Mg alloy is fabricated by hard-pate-rolling.•The bimodal sample has higher strength and ductility than fine-grained samples.•The synergy effect of fine and coarse grains on enhancing ductility is clarified.