Former Deputy Senate President, Ike Ekweremadu and Senator Ovie Omo-Agege are currently battling for the Deputy Senate President position.
About 107 lawmakers have already begun voting to choose from the duo.
Omo-Agege represents Delta Central Senatorial District, while Ike Ekweremadu represents Enugu-West.
Voting is expected to end before 1.30pm.
Omo-Agege was nominated as the deputy senate president by Katsina-North senator-elect, Ahmed Babba Kaita.
The nomination was seconded by Abdullahi Sabe of Niger-North.