In this study, structural properties of unexpanded perlite and expanded perlite particles were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis techniques. Electrokinetic properties of unexpanded perlite and expanded perlite particles in polar (water) and non-polar (silicone oil) media were determined using zeta ()-potential measurements as functions of time, pH, valences of electrolytes, type of surfactants, and temperature. Antisedimentation stabilities of the unexpanded perlite and expanded perlite particles dispersed in silicone oil were determined as a function of temperature at various volume fractions (phi=5%-25% v/v). Viscoelastic properties of expanded perlite particles dispersed in silicone oil were investigated by creep and creep-recovery tests under externally applied electric field strengths. As a result, the -potential and antisedimentation stability values revealed that colloidal stabilities of the expanded perlite particles were high enough to be used as smart electrorheological material in long time durations. Expanded perlite/silicone oil dispersion behaved as a viscoelastic material and exhibited a reversible nonlinear viscoelastic deformation under applied electric field and showed a vibration damping capability for potential industrial applications.