Selective monohalogenation reaction of unsymmetrical zirconacyclopentadienes was developed by selective protonation and iodination reactions. Among the examined acids, acetic acid and acetylacetone showed the best yield and selectivity to afford the corresponding monoiododienes. For the zirconacyclopentadiene prepared from 3-hexyne and diphenylacetylene, the Et-bearing carbon-zirconium bond was selectively protonated with more than 90% selectivity.