Density functional perturbation theory calculations have been performed to determine the dielectric constant of Si "doped" polyethylene (PE). Substitution of C atoms in PE by Si ranging from 0 to 100% has been considered. Both the electronic and ionic contributions to the dielectric constant increase with increasing Si content. These increases are attributed, respectively, to enhanced sigma conjugation and increased IR vibrational intensity of modes involving Si containing bonds (owing to their softness and polarity).