The mechanism of ionic conductivity (σ) in pure and doped polyvinyl chloride (PVC) with 30 % Al2O3 has been investigated from the viewpoint of free volume. Free volume was quantified using the positron annihilation lifetime (PAL) technique and ionic conductivity was measured as a function of temperature in the range from 30 to 140 oC. Positron annihilation lifetime of pure and doped PVC with Al2O3 reflect the effect of concentration as well as temperature on hole volume. Good linear correlations between Log(σ)+∆Ea/2.303KT [∆Ea is the activation energy, K is the Boltizmann constant and T is the abolute temperature] and the reciprocal of the o-Ps hole volume size (1/Vo-Ps) at different temperature indicate that the ionic motion in pure and doped PVC with 30 % AL2O3 is controlled by free volume.