Background Combinatorial therapy including the immunotherapy is revolutionizing the effective treatment of cancer. It achieved unprecedented responses in advanced-stage patients, including complete cures and long-term survival. However, immunotherapy also has limitations, such as its relatively low response rates and the development of severe side effects. These drawbacks are gradually being overcome by improving our understanding of the immune system, as well as by establishing combination regimens in which immunotherapy is combined with other treatment modalities. Methods Herein, we report the method of coassembly of two structurally defined materials, each comprised of photothermal agent and a small molecule immunostimulant molecularly self-assembled. One organic polymer has excellent photothermal properties; the other one has designed for efficient immmune activation, contributing to superior stability during circulation. Results The coassembled nanoparticles (NPs) possesses superior photothermal conversion efficiency as well as efficient encapsulation and controlled release of cytotoxic molecules and immunomodulatory agents. NPs loaded with immunostimulant has proven to be a highly efficacious combination photothermal/immunotherapeutic nanoplatform against Triple Negative Bresat Cancer xenograft model. When loaded with imiquimod, a potent small molecule immunostimulant, NPs is found to be highly effective against breast cancer model, particularly when photothermal/immuno-therapy is given. Such dual therapy not only eradicates the light-irradiated primary tumours, but also activates systemic antitumor immunoactivity, causing tumour death at light-unexposed distant tumour sites. Conclusion In conclusion, this “photothermal immunotherapy” approach, photothermal ablation of tumour cell death reduces tumour growth and releases tumour antigens into the surrounding milieu, while the immunoadjuvants potentiate host antitumor immunity. Our results indicated that combined photothermal immunotherapy is more effective than either immunotherapy or photothermal therapy alone against primary treated and distant untreated tumours in a mouse breast cancer model. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure All authors have declared no conflicts of interest.