We have analyzed the [Fe II] and [Ni II] emission lines in the bipolar planetary nebula Mz 3. We find that the [Fe II] and [Ni II] lines arise exclusively from the central regions. Fluorescence excitation in the formation process of these lines is negligible for this low-excitation nebula. From the [Fe II]/[Ni II] ratio, we obtain a higher Fe/Ni abundance ratio than the solar value. The current result provides further supporting evidence for Mz 3 as a symbiotic Mira.