In this work, we investigated the effects of flow modifiers in glass fiber reinforced polyamide 66(PA 66/GF) composites. The flow modifiers were prepared from various fatty acid and amine monomers and then the torque and viscosity were examined according to the molecular structure. The structure of the synthesized flow modifiers were analyzed by FT-IR and NMR. PA 66/GF composites were fabricated by melt compounding at 280℃ and the prepared flow modifier was also compounded simultaneously. Mechanical and rheological properties of the composites were investigated by universal testing machine and capillary rheometer, respectively. The p-phenylene bis stearamide has good effect to reduce the torque in neat PA66 polymer, whereas hexamethylene bis stearamide shows the best effect to reduce the torque in glass fiber reinforced PA66 composites. In 50wt% glass fiber filled composites, the torque during compounding has decreased approximately 15% at 1phr concentration of hexamethylene bis stearamide, which is also supported by the spiral flow test. The hexamethylene bis stearamide improves spiral flow measured using injection molding without lowering flexural modulus. But there is 3% and 10% drop in tensile and impact strength respectively. An attempt has been made to investigate the role of flow modifier in influencing of the PA66/GF composites.