There are remarkable reactivity differences between mono-alkoxy zirconocene compounds and zirconocene dichloride. The cyclopentadienyl groups are generally inert to both nucleophilic and electrophilic reagent. But the cyclopentadienyl ligands are largely influenced by the other ligands. We obtained the fulvenes and the acylated fulvenes by reaction of mono-alkoxy zirconocene with aldehyde and studied the mechanism of these reactions.