Micron-size crystalline particles of Poly(ethylene terephthalate) (PET), obtained from PET bottles by crystallization and grinding, were used as a filler in high-density polyethylene (HDPE). The composite of PET particle-filled HDPE was prepared by melt mixing at 190 degreesC, which was well below the melting temperature of PET. Silane coupling agents (SCAs) were used to enhance the interaction between PET and HDPE in the composite. A chain extender (CE) and maleic anhydride (MA) were also used to provide further interaction with SCAs between these two materials. The ultimate tensile strength, especially at highest content 40% PET-filled HDPE, and the impact strength of SCAs-treated PET-filled HDPE was found to be highly improved compared to untreated PET filling into HDPE. Dynamic mechanical analyses (DMA) demonstrated that T-g of the main matrix polyethylene was depressed from 3 to 10 degreesC. Scanning electron microscopy (SEM) studies indicated a strong interaction between PET powder and HDPE when SCAs were present in the system.