The synthesis and gas-sensing properties of ZnO particles from an ionic liquid precursor benzyltrimethylammonium hydroxide (BTMAH) is studied. The BTMAH, acting as reactant precursor and solvent, is demonstrated to be effective for synthesis of ZnO particles with controlled morphologies. The effect of the water and zinc salt concentration on the morphology of the synthesized particles is investigated. The gas-sensing tests shows that the sensors based on the synthesized ZnO nanoplates exhibit excellent ethanol-sensing properties.