The usage of sepiolite muds is not common in the drilling industry even though they exhibit better rheological properties under high temperature and high salinity environments than those of rivals due to their unacceptable high filtration losses. Recent studies have revealed that it is possible to obtain low filtrate rates from these muds along with commercial additives under static conditions at harsh temperatures and saline environments. On the other hand, the dynamic fluid loss behaviors of sepiolite muds are not a well known phenomena. There is no published work on the dynamic filtration behavior of these muds. The main goal of this study is to characterize the dynamic filtration behavior of sepiolite muds formulated with commercial additives under elevated temperatures and pressures. In addition, effects of particle size gradation of sepiolite clay on dynamic filtration properties of these muds are investigated. The variation of spurt loss volume, dynamic filtration rate, and cake deposition index properties of sepiolite muds are investigated with a computerized dynamic filtration apparatus. Numerous dynamic filtration loss histories with a test duration of 45 to 60 minutes at temperature conditions ranging from 200 to 400 F, a filtration pressure of 100 psi (0.7 MPa), and only one sample with 500 psi (3.45 MPa) have been conducted. Three key parameters, namely, spurt loss volume, dynamic filtration rate, and cake deposition index to characterize the dynamic fluid loss of sepiolite muds were determined experimentally. The experiments have resulted in acceptable dynamic filtration rate and cake deposition index values for the fresh water sepiolite-based mud at high temperatures. The experimental results promise that properly formulated sepiolite muds can be a good choice in geothermal well drilling beside their low cost advantages.