Abstract：Polyhexamethylene terephthalamide (PA6T) is a kind of semi-aromatic polyamide with excellent performance. Glass fiber (GF) reinforced composites of PA6T’s random copolymer with polyhexamethylene adipamide (PA66) were prepared via melt blending method. In order to improve the inferior mechanical properties of the composites, silane coupling agent KH550 was also employed to modify the interfacial adhesion between resins and glass fibers. Differential scanning calorimetry (DSC) test results showed that with the addition of KH550 in composites, the melting temperature changed little while the melting enthalpy decreased obviously, besides, 30wt%GF caused a further decrease, which suggested a decline of the crystallization ability of the matrix. Thermogravimetric analysis (TGA) test revealed that the decomposition temperature of the composite materials had no obvious changes with different content of the GF. The initial decomposition temperature of composites contained various content of GF were about 406oC, keeping its initial excellent thermal performance well. Mechanical properties test showed when the content of GF was 30wt%, the tensile strength, flexural modulus and unnotched impact strength of composites was 96.1 MPa, 4944MPa and 18.0 kJ/m2 respectively, increased by 123%, 171% and 100% to the resin matrix correspondingly. On the other hand, those composites with 2wt% KH550 get additional increase by 53.5%, 102% and 224% in tensile strength, flexural modulus and unnotched impact strength respectively, comparing to the PA6T/66-30wt%GF composites. Due to the good interfacial adhesion provided by KH550, scanning electron microscope (SEM) results showed a rough fracture surface and GFs combined with the resin tightly, which contributed to the mechanical performance. Keywords: coupling agents; glass fiber; PA6T/66; composites; performance