As a promising alternative to thermoset elastomers, thermoplastic elastomers (TPEs) have attracted much attention because of their unique properties, including processability, reusability and recyclability. The synthesis of TPEs based on olefinic building blocks usually requires the use of long chain a-olefins, multiple steps, and/or multiple catalysts. The concept of using only ethylene as feedstock in a single step is fascinating but also very challenging. In this contribution, we report the synthesis of polyethylene-based TPEs through a-diimine nickel-catalyzed ethylene polymerization. The stress-at-break and strain-at-break values of these polyethylene products could be tuned over a very wide range using different nickel catalysts and different polymerization conditions. Most importantly, products with excellent elastic properties could be generated in the screening process.