The hysteretic behavior of a sliding seismic isolation system is basically a function of its friction properties. Thus, identification of the coefficient of friction at the sliding interface of the isolator is crucial. It requires displacement controlled dynamic tests to determine friction properties considering loading conditions representative of seismic actions. In these tests, the number of loading cycles is mostly three, and deterioration in friction coefficient, which is mostly due to frictional heating at the sliding interface, is assessed from cycle to cycle. The aim of this experimental study is to investigate the effect of vertical force and loading velocity on friction properties of a full-scale double friction pendulum. During the tests, by means of thermocouples mounted on the isolator, the change in temperature at the sliding interface was monitored too. Isolator tests were conducted at ESQUAKE Seismic Isolator Test Laboratory of Eskişehir Technical University. Results showed that the amplitude of frictional heating is highly dependent on the vertical force and the loading velocity. It is also revealed that the corresponding temperature rise at the sliding interface is not uniform. This is especially more pronounced for high loading velocities.