Incorporating of semiconducting metal oxides and carbonaceous materials reasonably has been proven to be an effective method to improve the sensing properties for gas sensors. In this work, the novel reduced graphene oxide-wrapped hollow SnO nanospheres (H-SnO@rGO) composites are successfully synthesized via a simple hydrothermal method without any templates added. This unique hybrid structure is demonstrated to show significantly enhanced formaldehyde sensing performance compared to the pristine SnO nanospheres. At an optimal temperature of 130°C, [email protected]%rGO sensor exhibits an ultrahigh response (435) to 10 ppm formaldehyde, which is more than 17 times higher compared to the pristine SnO. Besides, it delivers excellent selectivity, low detection limit and fast response/recovery time. The synergistic effect of SnO and rGO plays an important role in improving the sensing behavior. The enhancement mechanism responsible for the superior sensing properties of the nanocomposite is also discussed.