The main purpose of this paper is to investigate the feasibility of using high-intensity ultrasound beams for transkull brain tumor hyperthermia. An algorithm is developed to search for the appropriate aperture diameter and the input power level that induce both a well focused high intensity region and an effective thermal dose region to enhance the goodness of the brain ultrasound hyperthermia treatments. Results illustrate that the ratio of intensity at the tumor is always higher than that onto the outer bone surface and their differences become smaller for higher frequency. Results also indicate that for lower frequency the ratio of intensity (IR) at tumor location to those at the inner surface of skull is higher to treat deeper brain tumors. Simulation results demonstrate that (1) for a high-perfused brain tumor lower frequency and/or the larger diameter of aperture window have to be used; (2) the problems with a brain tumor close to skull bone or larger brain tumors become more difficult to solve.