Rutile-phased TiO2-filled polyethylene (PE/TiO2) composites with dielectric constant (εr) ranging from 3.2 to 10.45 have been prepared by melt-mixing method and hot-molding techniques. The dielectric constant and dielectric loss (tanδ) of PE/TiO2 composites show an increasing trend, whereas the relative density, coefficient of thermal expansion and tensile strength showed a monotonically descending trend with increasing the rutile-phased TiO2 contents. A comparison of experimental and theoretical results shows large deviation at high filler contents. The prepared rutile-phased TiO2-filled PE composites were well suited for microwave application, especially for its ultra-low loss tangent (< 1.0 × 10−3).