In this study, a new preparation method of hydroxy double salts (HDSs) including organic compounds between layers has been established in which the HDSs were prepared by reacting ZnO with organic metal salts in water. This method does not need an anion-exchange reaction to incorporate organic compounds into the HDS layers. Moreover, the reaction proceeds under mild conditions around room temperature, and the obtained HDSs showed high crystallinity compared to those obtained by an anion-exchange reaction. We prepared ZnO crystals having a thin-plate structure by the thermal treatment of hydroxy zinc acetate at 873 K.