ZnO was synthesized by using layered zinc hydroxide acetate (ZHA), as a precursor. ZHA was aged in zinc acetate (ZnAc), magnesium acetate (MgAc), and barium acetate (BaAc) aqueous solutions under hydrothermal condition. The effect of divalent metal ions, Zn2+, Mg2+ and Ba2+, on the morphology of ZnO was studied. Results show that thin and thick plate-like and rod-like ZnO particles were synthesized for aging in ZnAc, MgAc and BaAc aqueous solution, respectively. In addition, the length to the c-axis direction became smaller in ZnAc and MgAc solution, and longer in BaAc solution, respectively, by increasing the concentration. Zn2+ and Mg2+ complexes with hydroxide and acetate ion are stable in aqueous solution. They adsorb on the growth plane instead of the growth unit of ZnO, Zn(OH)42−, and would inhibit the c-axis direction growth. Thus, ZnO particles with shorter length are obtained. On the other hand, since Ba2+ complexes are unstable, Ba2+ ions would not affect the morphology of ZnO, and therefore ZnO particles with longer length are obtained. It is concluded that morphology of ZnO, especially the c-axis length, is controlled by selecting metal ions with appropriate complex stability constants.