We performed high–temperature friction experiments to investigate the effect of temperature on the frictional behavior of smectite and illite. Friction coefficients (μ) of these clay minerals increase with increasing temperature as a result of dehydration of absorbed and interstitial water. At a constant normal stress of 60 MPa, μ of Ca–smectite gouge increases from 0.27 at room temperature to 0.67 at 200 °C, and μ of illite gouge increase from 0.53 at room temperature to 0.68 at 200 °C. Velocity dependence of steady–state friction for smectite and illite gouges changes with temperature so that the transition from velocity–strengthening to velocity–weakening behavior occurs at 150 °C at a normal stress of 60 MPa. Temperature at which this change takes place corresponds to the temperature at the updip limit of the seismogenic zone along subducting plates. Thus, the effect of temperature on the frictional behavior of these clay minerals possibly play an important role in controlling the updip limit of subduction thrust earthquakes.