In this work, Rheological and mechanical properties of acrylonitrile – butadiene – styrene/ corn starch composites (ABS/starch) were studied. The composites were prepared using a laboratory scale single screw extruder. Rheological properties were determined using the single screw extruder, and apparent shear rate (γ), apparent shear stress (τ), apparent viscosity (η), non- Newtonian index (n) and flow activation energy at a constant shear rate (Eγ) and constant shear stress (Eτ) were determined. Mechanical properties in term of tensile tests were performed using Testometric M350-10KN, stress at break, strain at break and Young's modulus were determined. Rheological results showed that the composites are pseudo plastic in behavior, and the apparent viscosity of the composites increases with increasing starch content above the additive rule which indicates a partial compatibility in the composite, also it was found that the flow activation energy of the composite increases with increasing starch content. Also it was found that the activation energy value at a constant shear stress is more than that at a constant shear rate. The mechanical results showed that the strain at break of the composite decreases sharply by the presence of starch, whereas the young's modulus increases with increasing starch content.