Abstract Background Photothermal immunotherapy, as a promising technique in cancer treatment, offering precise eradication of tumor tissue, minimal adverse effects, and reduced risk of recurrence and metastasis. However, due to the instability of tracer function after photothermal immunotherapy, the long-term in vivo tracing is still a significant challenge, thereby greatly impeding the comprehensive assessment of immune response and drug delivery outcomes. Results Here, we successfully demonstrated the feasibility of stable long-term in vivo immune tracking of photothermal immunodiagnosis and immunotherapy for breast cancer. The biocompatible and stable Ag2S quantum dots, with an average size of 3.8 nm, were coated with ovalbumin (OVA) and loaded with immune adjuvant imiquimod (R837). This synthesized Ag2S@OVA-R837 nanovaccine exhibited an excellent photothermal response upon near-infrared irradiation at 808 nm and effectively activated dendritic cells. In an in vivo breast tumor mouse model, we demonstrated that this nanoplatform, in combination with laser treatment, significantly improved long-term survival rates, reduced tumor size, and elicited robust immune responses. Conclusions The results support that Ag2S@OVA-R837 is a promising photothermal immunotherapy (PIT) tracer nanoplatform to feedback immunoefficacy of therapeutics and holds great promise for precise treatment and diagnosis of malignant tumors, providing a novel avenue for visualizing the in vivo distribution and trafficking of functional therapeutics.