Composites based on rPE and OPEFB waste are considered sustainable materials. However, their performance is limited by hydrophobic–hydrophilic incompatibility, which weakens interfacial adhesion. This study investigated the atmospheric-pressure air plasma treatment of rPE to enhance its compatibility with OPEFB fibers and evaluated its role as a compatibilizer. Atmospheric plasma treatment for 120 s introduced oxygen-containing groups onto the rPE surface, as evidenced by C-O and OH peaks in the FTIR spectra and the higher O/C ratio in the XPS analysis. Consequently, the water contact angle decreased, reducing the difference in surface tension between rPE and OPEFB from 45.61% to 7.80%. Composites containing 20 wt.% OPEFB were fabricated by varying the proportion of untreated rPE with p-rPE. All p-rPE-based composites exhibited fewer interfacial voids than untreated rPE composites, indicating improved fiber–matrix adhesion. The tensile strength and elastic modulus increased with the p-rPE content, whereas the elongation at break remained higher than that of the untreated composite. Therefore, p-rPE shows potential as a compatibilizer, enabling agricultural and plastic waste value enhancement. © 2026 by the authors.