Different scanning calorimetry and dynamic mechanical analysis are used to study the thermal behavior of composites by melt-mixing low-density polyethylene (LDPE) matrix and zinc oxide whisker (ZnOw) fillers. Micrographs of the composites illustrate that needle or wedge shaped ZnOw are distributed uniformly in the LDPE matrix. Dielectric properties of the composites are measured in a frequency range of 1-10 MHZ. The results show that the addition of ZnOw does not affect the melting behavior of LDPE, but has an important effect on the heat of fusion, dynamic mechanical behavior, and dielectric behavior of the composites.