In most developed countries, cancer is presently responsible for about 25% of all deaths. Heat therapies like hyperthermia and thermoablation are very promising approaches in the treatment of the cancer. Since these are physical treatment methods they have fewer side affects compared to chemo- and radio-therapy. Currently, various types of heat treatment modalities are available like microwave, ultrasound, RF capacitance hyperthermia, RF probe hyperthermia, magnetic fluid hyperthermia, but non of these methods have the ability to accurately deliver high heat energy to deeply seated tumors without damaging the healthy surrounding tissues. In this thesis, a novel RF ablation system was developed capable of focusing the heat in to very small areas in the order of millimeters, which will allow heating of the tumors without destroying collateral normal tissues. Generally, in this system the tumor ablation is achieved via coupling RF energy on the magnetic fluids which are previously dispersed in to the tumor tissue. By considering the human safety limits (nerve stimulation and tissue eddy current heating safeties) optimum treatment parameters like particle size of the magnetic fluids, frequency and strength of the applied RF field are obtained. The utilization of the optimum parameters may lead to the very effective operation of the ablation system where treatments can be done with very small amounts of fluid injections, in short durations. We believe that by the studies conducted in this thesis, magnetic fluid hyperthermia (tumor ablations using magnetic fluids) can be a much more effective method so that it can be used as the one of the most important tumor treatment techniques in future.