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To enhance the thermal stability and mechanical properties of co-polyamide (CO-PA), a sequence of nanocomposites based upon CO-PA and shear exfoliation graphene (SEG) were prepared via a simple solution mixing method. The graphene used as nanofiller was fabricated by shear exfoliation in aqueous phase and is free of basal-plane defects. Atomic force microscopy and scanning electron microscopy revealed that the graphene fabricated is few-layer graphene rather than solely monolayer graphene. X-ray diffraction and polarizing microscope indicated that SEG layers could change the crystallization behavior of the nanocomposites and conduce to the crystal form transformation. The CO-PA/SEG nanocomposites were found to be of outstanding thermal stability and mechanical properties at extremely a low graphene loading as opposed to neat CO-PA. In detail, at a graphene load of 0.05 wt%, the nanocomposites present 106.5, 56.1, and 33.7% enhancement in tensile strength, yield strength, and elongation at break compared to pristine CO-PA, respectively. Besides, thermal degradation temperatures at 50% weight loss of the nanocomposites is about 19°C higher than that of CO-PA when the SEG content is 0.15 wt%; the thermal degradation temperature at maximum weight loss rate of the nanocomposites is 25°C higher than that of CO-PA when the content of SEG is 0.20 wt%. All these enhancements of the nanocomposites were ascribed to the defect-free graphene, its superior thermal and mechanical properties, and its well exfoliation and dispersion in CO-PA matrix.