In the present work, cetyltrimethylammonium bromide (CTAB)-treated sawdust-reinforced recycled polyethylene (RPE) composites were prepared by injection molding method. The mechanical properties of RPE composites reinforced with CTAB-treated sawdust were evaluated and the results were compared with those of untreated ones. The tensile strength (TS) values of the CTAB-treated composites were found to be much higher than those of the untreated ones. The Young's modulus (YM), flexural strength (FS), flexural modulus (FM), and hardness values were also found to be improved for the treated sawdust RPE composites compared to those of the untreated ones. The tensile fracture surface morphological features of treated sawdust RPE composites observed by scanning electron microscopy (SEM) revealed less microvoids and fiber agglomerates, indicating that better fiber matrix interfacial adhesion has occurred upon treatment of the sawdust with CTAB. Water absorption (%) values were found to increase with increases in fiber content in the composite. However, treated sawdust RPE composites showed lower water uptake capacity compared to those prepared from untreated sawdust. From the IR spectra of raw and treated sawdust together with water absorption behavior of the composite specimens, it appeared that surface treatment with CTAB significantly reduced the hydrophilic nature of sawdust, resulting in improved fiber matrix interfacial adhesion.