The ionic conductivity a of PMMA-based gels with and without nano-particle filler has been investigated at elevated pressure up to 0.9 GPa and in the temperature range 220-330 K to determine the effect of pressure and to obtain the activation volume. Both gels had molar ratios: EC:PC:LiCIO4:PMMA 53.9:22:5.2:18.9, and one gel contained 8 wt.% TiO2 nano-particles. At room temperature and atmospheric pressure, the conductivity of the gel with filler is almost the same as that for the gel without filler. At increasing pressure p, (T(p) for both gels exhibits an abrupt change, which is associated with a transition, and consequently there is a pressure induced change in the activation volume for both gels. The activation volume &UDelta; V* in low-pressure state is the same for the gels with and without filler and about 14 cm(3) mol(-1) at room temperature, which is typical liquid-like behaviour. In the high-pressure state, &UDelta; V* = 42 and 45.3 cm(3) mol(-1) at 294 K for the gels with and without filler, respectively. The results show that the ionic movements are restricted by the rigid environment of the high-pressure state and that the filler affects A V under this condition. In particular, the filler appears to improve the cation transport number as a results of a decreased mobility of large-sized ions in the rigid environment of the high-pressure state. © 2004 Elsevier Ltd. All rights reserved.