Ujah was on the books of the German Bundesliga side in the 2011-12 season before transferring to FC Cologne where he spent three years.
36 goals in 102 appearances for the Billy Goats earned him a move to Werder Bremen where he scored 14 times in 37 competitive duels. And in the summer of 2016, the 27-year-old moved to China to team up with Liaoning.
Swayed by his return to the Opel Arena, sports director, Rouven Schröder said: "Anthony Ujah is an athletic, determined and strong attacker who has proved his qualities at the Bundesliga level and adds real value to our squad, and he is a great character and will not be due to his Mainz past.
"We need to make sure that he has decided on a future at Mainz 05."
The striker, excited with the switch, said: "I am very happy that I return to Mainz because I have only good memories of my time there, I am looking forward to the Bundesliga as well and I want to help the team from the second half of the season to reach."
Ujah will team up Super Eagles teammate and defender, Leon Balogun - who already took to Twitter to express delight at the prospect of playing alongside the striker in Sandro Schwarz’s team.
“Oh boi!!! Welcome back in Mainz and to the Bundesliga looking forward to play with you again brother Anthony Ujah,” Balogun tweeted.
“Thanks for the early Christmas present Mainz 05.”
Ujah will be looking forward to adding to his two-goal tally in 12 league appearances for the O-Fives when he starts his second stint in January.