Self-reinforced polyethylene composites have proven to be promising candidate materials for a number of wear-resistance and bioimplant applications. In this study, we investigated the effects of processing parameters on the elastic modulus of self-reinforced high-density polyethylene (HDPE) composites. The processing parameters investigated were the cooling rate, processing pressure, temperature, and duration. Our results showed an optimum processing temperature, pressure, and duration that were matrix-dependent. In addition, for an HDPE matrix, the slower the composite cooling rate was, the higher the composite modulus was.