In organic chemistry, ethenolysis is a chemical process in which internal olefins are degraded using ethylene () as the reagent.  The reaction is an example of cross metathesis.  The utility of the reaction is driven by the low cost of ethylene as a reagent and its selectivity. It produces compounds with terminal alkene functional groups (α-olefins), which are more amenable to other reactions such as polymerization and hydroformylation.
The general reaction equation is:
Ethenolysis is a form of methylenation, i.e., the installation of methylene () groups.