To evaluate the effect of thermoseed inductive heating on mammary orthotopic transplantation tumors and immunologic function in rats. Walker-256 tumor cells were inoculated subcutaneously into the mammary glands of Wistar rats. Rats were allocated to five treatment groups as follows: i) C group (control group); ii) M group (magnetic field group); iii) T group (thermoseed control group); iv) H1 group (hyperthermia treatment, 45 degrees C for 30 min); v) H2 group (hyperthermia treatment, 50-55 degrees C for 10 min). Immediately, 12 and 24 h after hyperthermia, two rats were sacrificed in each group for pathological and immunohistochemical examination of the expression of PCNA and HSP70. Tumor volume was measured and long-term survival was observed. The T lymphocyte subgroup IL-2 and IFN-gamma levels were measured in C, H1 and H2 groups. Both types of hyperthermia induced necrosis and apoptosis in the tumor tissue, decreased tumor volume (P<0.05), and increased survival time (P<0.01). The expression of PCNA and HSP70 in hyperthermia group was significantly different compared to the C, M and T groups (P<0.05), Hyperthermia increased CD4+ T lymphocytes and the levels of IL-2 and IFN-gamma (P<0.05). Both types of hyperthermia can suppress the growth of mammary tumors and improve immunological function of rats.