Poly(phenylene sulfide) (PPS) is an attractive polymer in engineering plastics because of its high mechanical strength and thermal stability. Herein, poly(phenylene sulfide)/nylon 6 grafted graphene oxide (PPS/NGO) nanocomposites were prepared by micro-compounding, where NGO is prepared via ring-opening polymerization of ε-caprolactam on the graphene oxide (GO), which has carboxylic acid groups that can act as an initiator. Since nylon 6 is known to be able to blend with commercial PPS, nylon 6 moiety in NGO can increase mechanical properties of PPS, especially by forming PPS/NGO nanocomposites with improved toughness. Moreover, graphene nanosheets can provide improved mechanical strength and thermal stability because of their mechanically reinforcing and thermal barrier effects. For example, if a PPS/NGO nanocomposite with 0.03 wt% of NGO was prepared, the tensile strength and elongation at break values increased by 32% and 30%, respectively, compared to neat PPS. Also, the thermal decomposition temperature for 5% weight loss increased from 481 to 488 °C, indicating the improved thermal stability. These improved properties can be attributed to the well-dispersed NGO in the PPS matrix, as confirmed by the morphological studies using SEM and EDS mapping.