High-intensity focused ultrasound (HIFU) therapy offers great promise for the treatment of cancer. The histological changes, including the antitumor immunological response, after HIFU treatment was examined in soft tissue sarcoma. Sarcoma 180 cells were injected subcutaneously in mice. Approximately 2 weeks after the injection, the tumor was irradiated by a single shot of HIFU. The tumor diameter was measured and the survival rate was observed after treatment. The tumors were resected, and stained with TUNEL stain, tartrate-resistant acid phosphatase (TRAP) stain to detect tumor-associated macrophages, and immunohistochemical stains for CD4 and CD8. The tumor size in the HIFU group was significantly smaller than the control and survival rate was significantly higher. The numbers of TUNEL-, TRAP-, CD4- and CD8-positive cells infiltrating the tumor were significantly higher in the HIFU group. HIFU, even when administered as a single shot, induces apoptosis of tumor cells and intratumoral infiltration of macrophages and lymphocytes.