Here, we report the first example of preparation of polyethylene (PE)/exfoliated-MoS2 nanocomposites through in-situ Ziegler-Natta polymerization. The exfoliated-MoS2/MgCl2-supported Ti-based Ziegler–Natta catalyst was synthesized via a facile coagglomeration method. The effects of MoS2 on the catalyst morphology and the ethylene polymerization behavior were examined. The resultant PE/MoS2 nanocomposites had a flake shape morphology, and the MoS2 fillers were well dispersed throughout the entire PE matrix. In addition, the thermal stability and mechanical properties of the PE base material were significantly enhanced by the introduction of a very small amount of the MoS2 filler (0.08 wt%). Therefore, this work provides a facile method to produce of high-performance PE.