Dendrimers are polymeric compounds with highly branched structures and functionally tunable peripheral groups. Because of their low polydispersity, high degree of molecular uniformity, and precisely controlled structure, dendrimers are excellent models for demonstrating a variety of biological activities. With the attachment of metals ions and/or metals, metallodendrimers or dendrimer nanocomposites, respectively, provide diverse characters for a variety of applications. Functionalization with additional moieties, such as targeted peptides or chromophores, yields metallodendrimers that can find powerful applications and exceed the capabilities of nondendritic molecules or small molecule analogs. This review introduces the background of metallodendrimers and dendrimer nanocomposites. Biomedical applications of metallodendrimers and dendrimer nanocomposites will be discussed, including biomimetic catalysts, imaging contrast agents (especially for MRI imaging), or biomedical sensors and therapeutic agents.