A self-metathesis process for the production of unsaturated dicarboxylic fatty diacids and/or unsaturated dicarboxylic fatty diesters, wherein unsaturated carboxylic fatty acids and/or esters of unsaturated carboxylic fatty acids are reacted in the presence of at least one defined ruthenium based catalyst compound. A catalyst enhancer compound selected from a sacrificial catalyst or a non-catalyst enhancer may also be used. The process exhibits improved reaction times and/or the catalyst can be used at very low concentrations.