The 29-year-old midfielder had been linked with a move to Esteghlal but opted to join Saipa.
Mosalman played in Sepahan last season but left the team at the end of the league.
Esteghlal coach Mahmoud Fakri had confirmed that they would think about signing Mosalman for the new season.
The new edition of the Iran Professional League will kick off on November 6.
Saipa will meet titleholder Persepolis on Friday.