Chemoimmunotherapy can boost strong antitumor immune responses by triggering immunogenic cell death (ICD), which highlights a promising prospect in clinical applications. However, current chemoimmunotherapy shows limited efficacy due to the low delivery efficiency and insufficient immunogenicity of available chemotherapeutic drugs. A supramolecular polymeric nanomedicine (Pt-Tu@NP) is herein reported using cucurbit[7]uril-based host–guest recognition and noncovalent self-assembly. Pt-Tu@NPs have excellent biodistribution and strongly evoke the endoplasmic reticulum stress-mediated ICD of tumor cells, triggering potent antitumor immune responses by promoting dendritic cell (DC) maturation and cytotoxic T cell infiltration. The coordinated butyrate promotes a positive feedback regulation between DCs and CD8⁺ T cells. Pt-Tu@NPs stimulate immune cold tumors into hot ones, working in synergy with an immune checkpoint blockade to effectively suppress tumor growth and metastasis, which suggests a promising approach for cancer chemoimmunotherapy.