Two kinds of zinc oxide (ZnO) powders, which are ZnO whisker (w-ZnO) and nanosized ZnO (n-ZnO), were used to prepare the composites with a matrix of low-density polyethylene (LDPE). Dielectric constants and losses of the composites were measured- in a frequency range of 1-10 MHz. The dielectric constants and losses increase with increasing w-ZnO content in composites. Modified w-ZnO has a remarkable effect on dielectric properties of the composites. Dielectric constants and losses of the composites containing n-ZnO are larger than those containing w-ZnO under the same content. The results can be explained by nanoscale effects. Some theories of mixing laws are also referred to the dielectric properties of composites in this paper. (C) 2002 Elsevier Science Ltd. All rights reserved.