The 22-year-old moved to the Estadio da Luz last year after a three-season spell at Heerenveen in the Eredivisie.
Djuricic made 21 appearances for Benfica in all competitions last term, but started just five league games as Jorge Jesus' men lifted their 33rd league title.
He will spend next season at the Coface Arena and, like last term, ply his trade in the UEFA Europa League after Mainz finished seventh.
Christian Heidel, sporting director at Mainz, thinks the Serbia international - who was overlooked for his country's World Cup squad in Brazil - will make an exciting addition to Kasper Hjulmand's squad.
"Filip Djuricic is a young player who has made strong performances at top European teams," he told the club's official website.
"We're happy that he's joining on a one-year loan basis and has the chance to develop as a footballer with us."
Hjulmand, who replaced Thomas Tuchel in May, added: "He is a very talented player, nimble and dangerous in front of goal, who can raise the bar in the team.
"He will give our offence a lot of variability with his versatility."