Abstract: Investigating temperature distribution in biological tissues produced by microwave hyperthermic antennas is very important for designing antenna and deciding the treatment scheme in clinic hyperthermia. In this paper, the electromagnetic fields in biological tissues were simulated using the finite-difference time-domain (FDTD) method, while the bioheat equation was numerically solved using the finite difference. The simulation results of the temperature distribution for an monopole antenna insert muscle-equivalent phantom have been compared with experimental results, and they are coincided well.