Cancer remains one of the leading causes of mortality worldwide, and its early diagnosis and effective treatment have long posed a major challenge in the biomedical field. Conventional cancer diagnosis and treatment strategies are plagued by inherent limitations, which greatly restrict their capacity to meet the clinical demands of personalized and precision medicine. Metal-based nanomaterials offer unique advantages in cancer theranostics due to their unique quantum size effect, surface effect, and interfacial effect. These applications cover multiple aspects, such as multimodal imaging, tumor biomarker detection, photothermal therapy (PTT), chemodynamic therapy (CDT), and radiotherapy sensitization. Three‑dimensional (3D) printing enables the precise fabrication of complex architectures tailored to the personalized anatomical characteristics of tumor lesions, thereby effectively overcoming the drawbacks of metal-based nanomaterials, like uneven dispersion and inadequate tumor targeting. The integration of 3D printing technology with metal-based nanomaterials gives full play to their synergistic strengths, facilitating the construction of an innovative theranostic system characterized by customizable structure, tunable function, and integrated diagnosis and treatment. This review systematically summarizes the classification and underlying theranostic mechanisms of metal-based nanomaterials, mainstream 3D printing techniques suitable for such nanomaterials, and corresponding composite design strategies. It also outlines the latest research progress of this integrated platform in the diagnosis and treatment of prevalent malignancies. Furthermore, the current challenges and future research prospects in this field are discussed. This work aims to provide a reliable reference for further fundamental research and clinical translation of 3D printing combined with metal-based nanomaterials in oncological theranostics.