The contract runs through the end of the 2025-26 Iran Pro League season and includes a renewal option.
He has replaced Vahid Hashemian in Persepolis.
Under the leadership of Hashemian, Persepolis recorded two wins, one defeat, and five draws in eight games.
Loss previously managed Persepolis in 2024. During his brief spell in Tehran, he steered Persepolis to the Persian Gulf Pro League title.
“I have important goals for this season. I have big dreams in Persepolis but when one person makes dream it’s hard to reach in a team but if all people have the same dream, it will come true,” Osmar said.