The change in adsorption-induced electrical conductivity of some ferrocene derivatives as a function of temperature has been studied under moderate pressures. At a constant cell temperature, the conductivity of the pure ferrocene derivatives in the dry state depends an the applied pressure and this pressure dependence of conductivity is significantly different for different materials. A spectacular change in the electrical conductivity behaviour of these materials at the vapour-adsorbed state, as a function of temperature under mechanical pressure, has been observed. Pressure-induced change in conductivity of different ferrocene derivatives at the vapour-adsorbed state is remarkably different. The results have been discussed in the light of different existing theories. The unusual variation of conductivity with temperature under pressure is thought to be due to the phase transition in these materials.