Overproduction of reactive oxygen species (ROS) is commonly known as a key factor in the progression of many chronic inflammation diseases such as atherosclerosis and rheumatoid arthritis. In this study, a metal oxide nanodot-coated layered double hydroxide (LDH) nanocomposite is constructed for theranostics of ROS-related diseases. This is the first time that both cerium oxide and iron oxide nanoparticles (NPs) were attached on the surface of LDH NPs through electrostatic interaction via a nanoengineering approach. LDHs served as nanocarriers, cerium oxide NPs served as therapeutic agents due to the antioxidant properties, and iron oxide NPs served as magnetic resonance imaging (MRI) contrast agents. In vitro studies have demonstrated that the constructed nanocomposites have good biocompatibility, good antioxidant capacity to reduce ROS level in the cells, as well as satisfying cell imaging effect in MRI. Functionalization of LDH surface with cerium oxide NPs and iron oxide NPs allows the simultaneous therapy and diagnosis of ROS-related diseases and may also allow biodistribution tracking of the therapeutic cerium oxide NPs.