| Leopold Horner | |
| Birth Date: | 24 August 1911 |
| Birth Place: | Kehl, German Empire |
| Nationality: | German |
| Death Place: | Mainz, Germany |
| Work Institution: | University of Munich, University of Mainz |
| Alma Mater: | University of Munich |
| Doctoral Advisor: | Heinrich Wieland |
Leopold Horner (24 August 1911 - 5 October 2005) was a German chemist who published a modified Wittig reaction using phosphonate-stabilized carbanions now called the Horner–Wadsworth–Emmons reaction (HWE reaction) or Horner-Wittig reaction.
Horner started studying chemistry at the University of Heidelberg and later with Heinrich Wieland at the University of Munich. After he received his Ph.D and his habilitation he worked at the Polymer Research Institute in Frankfurt. In 1953 he became professor at the University of Mainz.