Polyamide 6 (PA6)/polydimethylsiloxane (PDMS) blends exhibit high heat resistance as well as excellent oil resistance, which are suitable for automotive under-the-hood applications. However, PDMS and PA6 are immiscible. Their blends tend to undergo phase separation and yield poor mechanical properties. To address this challenge, this work uses an amine-terminated triblock copolymer of polyetheramine (PEA) and polydimethylsiloxane (PDMS) (PEA-PDMS-PEA) as a reactive compatibilizer for PA6/PDMS blends. The amine in this triblock copolymer can react with PA6 to in-situ form a copolymer of PA6 and PDMS which suppresses the coalescence of the dispersed phase. The addition of PEA-PDMS-PEA can significantly decrease the size of the dispersed PDMS domains in the PA6/PDMS blends. Organo-montmorillonite (OMMT) as a second additive can further decrease the size of the dispersed phase domains. Moreover, the synergetic effect of the OMMT and the reactive compatibilizer shortens the blending time necessary for reaching the ultimate domain size compared with separate addition of the OMMT and the reactive compatibilizer. The simultaneous addition of the OMMT and the reactive compatibilizer greatly improves the mechanical properties of the PA6/PDMS blends and decreases water absorption.