In the current study, the effects of three different silane coupling agents, namely (3-aminopropyl) triethoxysilane (AP), (3-Glycidyloxypropyl) trimethoxysilane (GP) and (3-trimethoxysilyl) propylmethacrylate (MA) are investigated on the mechanical properties of the basalt fiber (BF) reinforced poly (butyleneterefthalate) (PBT) composites. The tensile, flexural, impact, thermomechanical and morphological properties of the composites are investigated. According to the test results, the remarkable increase in tensile strenght and elastic modulus is observed, whereas slight improvement in flexural strenght and no change in impact properties is observed. According to flexural strength and elastic modulus values, the effectiveness of the silane coupling agents can be ranked as follow: GP > AP > MA. It is clearly shown that the increase in mechanical properties arises from improvement in interfacial adhesion between BF and PBT. It is concluded that the covalent bond formation causes the highest improvement in mechanical properties including tensile and flexural strenght and elastic modulus.