The simultaneous measurement of the acoustic pressure and the temperature at the focus of high intensity focused ultrasound (HIFU) in a tissuemimicking phantom were performed by using a dual sensing fiber-optic hydrophone (FOH). The HIFU pressure and the HIFU-induced temperature rise at the focus in the phantom were numerically simulated by using a MATLAB-based software package developed for HIFU simulation. The measurements of the HIFU-induced temperature rise showed good agreement with the simulations. It was also found that the presence of the FOH tip at the focus in the phantom did not affect the formation of a thermal lesion.