As previously reported,graphene showed the potential to sense many kinds of gases, such as NO2, CO, and so on. Here, the room temperature gas sensing properties of ZnO QDs/graphene nanocomposite were detected by choosing formaldehyde (HCOH) as the targeted gas molecule. Formaldehyde is a common indoor air pollutant and harmful to human beings health even at very low concentrations in the ppb scale.