Sarkozy telephoned Clotilde Reiss as she was celebrating Christmas in the French embassy in Tehran, where she has stayed since being granted bail in August.
"The head of state assured her of his total support and said he hoped to see her return to France soon to be with her own people," the Elysee palace said in a statement.
Iranian authorities have put Reiss, 24, on trial for allegedly taking part in protests that erupted in the wake of Iran's disputed presidential election in June.
Reiss was arrested in the wake of the protests that followed Iran's disputed presidential election in June, shortly before she was due to fly home after a six-month study and teaching visit to the city of Isfahan.
She was accused of supporting the opposition protests and was one of scores of people paraded before cameras at a televised show trial, before being remanded in custody in Tehran's notorious Evin jail.
She was bailed in August and is staying at the French embassy awaiting the outcome of her case.
France has furiously protested Reiss's innocence on all charges and has accused Tehran of trying to blackmail Paris into releasing an Iranian agent jailed in France for the 1991 murder of an exiled former prime minister.
Earlier in the day, France's Foreign Minister Bernard Kouchner also spoke to her by phone.
"He was able to learn that she is in good form, that her morale is good and that all the personnel of our embassy in Tehran are at her side," a foreign ministry spokesman said.
Kouchner reminded Reiss that "our aim is to see her return home as quickly as possible," he said.
French officials had hoped that a hearing on Wednesday would be the last that Reiss would have to face before her judge reaches a verdict, but her lawyer said afterwards that there would be at least one more session.
In an interview with AFP, Iranian President Mahmud Ahmadinejad said Tehran would like to free Reiss, but such a move would depend on the attitude of the French leaders.
