Splenomegaly is an enlargement of the spleen, which usually causes infectious mononucleosis and portal hypertension. In this study, a new inductive thermotherapy system for minimal invasive surgery (MIS) was reported for treatment of splenomegaly. It can generate a high-frequency alternating electromagnetic field to induce a localized temperature increase by inserting a two-part needle into the spleen. To prevent the overheating, a temperature feedback control system was developed such that the treatment can be operated at a safe and effective temperature. The relationship between the coagulation zone and the operating temperature/time was first explored. Then Lan-Yu pigs' spleen under the ultrasonic guidance was heated by using the developed system. The experiments showed that the developed electromagnetic thermotherapy system can successfully cause the atrophy of the spleen, which is very promising for further clinical use.