Poly(butylene terephthalate) /high density polyethylene (PBT/HDPE) blends and PBT/HDPE-grafted maleic anhydride (PBT/HDPE-g-MAH) blends were prepared by the reactive extrusion approach, and the effect of blend compositions on the morphologies and properties of PBT/HDPE blends and PBT/HDPE-g-MAH blends was studied in detail. The results showed that flexural strength, tensile strength, and notched impact strength of PBT/ HDPE blends decreased with the addition of HDPE, and flexural strength and tensile strength of PBT/HDPE-gMAH blends decreased, while the notched impact strength of PBT/HDPE-g-MAH increased with the addition of HDPE-g-MAH. Compared with PBT/HDPE blends, the dimension of the dispersed phase particles in PBT/HDPEg-MAH blends was decreased and the interfacial adhesion was increased. On the other hand, the effects of HDPE and HDPE-g-MAH contents on the crystalline and the rheological properties of the blends were also investigated. (c) 2006 Wiley Periodicals, Inc.