In an attempt to explore a convenient and efficient strategy for constructing tumor-targeted T₁ macromolecular contrast agents for magnetic resonance imaging, hyperbranched poly(glycerol) with good biocompatibility was used as a nanoplatform to conjugate gadolinium chelates and folic acid ligands through “click chemistry”. This macromolecular contrast agent presented high relaxivity relative to small molecule contrast agents and exhibited negligible toxicity estimated in vitro and in vivo. MRI measurements on tumor cells and tissue showed obvious targeting specificity. Moreover, a prominent positive contrast effect and a considerable time window for imaging were achieved at tumor location after tumor-bearing mice were intravenously injected with this macromolecular contrast agent. These promising results demonstrate the potential of hyperbranched poly(glycerol) as a T₁ macromolecular contrast agent for tumor-targeted MRI.