Cross-linked polyethylene (XLPE) is used as insulator coating in electrical wires and cables. Incorrect disposal of XLPE waste poses serious environmental problems since this cross-linked material is not recyclable through remelting, as is the case of thermoplastic polymers. Therefore, almost all the waste is burned or disposed of in landfills. An alternative to reuse XLPE waste is by micronizing and incorporating the micronized particles as filler in a thermoplastic matrix. In the present work XLPE was micronized and sifted to separate the particles in average sizes of 100, 500 and 900 micrometer. After sifting, sheets of XLPE concentrates in high-density polyethylene HDPE were produced, using a calendaring process. The sheets were ground and incorporated into HDPE by means of a twin-screw co-rotating extruder and subsequently injection molded into test specimens. A 2 by 2 factorial design with center point was used, where XLPE contents varied between 1 and 9 wt% and average particle size between 100 and 900 micrometers were assessed as to the effect of XLPE content and particle size on HDPE mechanical properties. Increase in XLPE content significantly increased only impact strength, and decreased tensile and flexural strength, and flexural modulus. The effect on tensile modulus and strain at break was not significant for the adopted 95% confidence interval. The increase in XLPE average particle size affected positively only impact strength of the material, and decreased strain at break and flexural modulus. The effect on tensile and flexural strength and on tensile modulus was not significant for the adopted 95% confidence interval. The interaction between the two variables decreased impact strength and increased tensile modulus, and was not significant for the other investigated properties.