Objective To evaluate the heating ability of thermoseeds in alternating magnetic field and its therapeutic effects on tumor bearing rats with simultaneously detected immune function. Methods To monitor the temperature increase of thermoseeds in vitro,of which the Curie point was 57 ℃ or 70 ℃.Forty Wistar rats implanted with Walker-256 cells were randomly divided into five groups: C group(control group,10 rats),M group(magnetic control group,5 rats),T group(thermoseeds control group,5 rats) and two heating treatment groups(H1 group,10 rats and H2 group,10 rats).In the H1 group,two thermoseeds with a Curie point at 57 ℃ were implanted into the tumor tissues in each rat with a heating time of 30 minutes,while in the H2 group,two thermoseeds with a Curie point at 70 ℃ were used with a heating time of 6 minutes.Five rats from each group were killed 9 days after the heating therapy to evaluate the volume and weight of the tumor tissues.The peripheral blood T-cells were counted in the rest rats in the H1,H2,and C groups. Results Magnetic inductive heating of the thermoseeds in vitro can reach the Curie point.The median tumor volume in the H2 group was 0.50 cm3(0.00-26.54),which was significantly lower than that in the M group(36.18 cm3,0.96-39.90,Z=2.21,P=0.032).And the weight of the tumors in the H1 and H2 groups was significantly lower than that in the M group [0.96 g(0.00-21.18) in H1 and 0.41 g(0.00-23.40) in H2 vs 31.45 g(1.09-36.09) in M group,Z=2.21 and P=0.032 for both].In the peripheral blood,the percentage of CD4+ T-cells was(22.39?5.27)% in H1 group,and(24.76?5.19)% in H2 group,which were significantly higher than that in C group [(12.07?4.45)%,P=0.01 and 0.003 respectively];and the percentage of CD8+ T-cells in the H2 group was significantly higher than that in the C group [(19.58?4.63)% vs(12.72?3.96)%,P=0.04].Conclusions Thermoseed had a good heating ability in alternating magnetic field and its inductive heating can inhibit tumor growth in Wistar rats and improve the immune function of the rats.