A Ziegler-Natta catalyst is a catalyst used in the production of unbranched, stereoregular polyalkene polymers. Ziegler-Natta catalysts are typically based on titanium tetrachloride and the organometallic compound triethylaluminium.

These catalysts were discovered in the 1950s by Karl Ziegler, who used a mixture of the above compounds to catalyse the polymerisation of ethylene. Giulio Natta, using the same mixture to catalyse propylene, discovered that the process gave a stereoregular polymer, that is, one with a regular arrangement of side chains.

This stereoregularity is believed to follow from a polymer growth mechanism known as the Cossee-Arlman mechanism, in which the polymer grows at vacant Cl sites at the Ti surface. In the search for a deeper understanding and control of Ziegler-Natta polymerisation at the molecular level, a number of metallocene catalysts have been developed, often offering fine control over the composition and tacticity of the polymer chain so produced.