"We are very likely to come to an agreement by the end of July," Rouhani told reporters in Shanghai, speaking in Farsi through a translator. "We can achieve this."
His comments came after an apparently largely fruitless fourth round of negotiations in Vienna last week.
But the UN atomic watchdog said yesterday that Iran has agreed to address some of the many long-held allegations that it conducted research into making nuclear weapons before 2003 and possibly since.
"It takes time" to resolve outstanding issues, Rouhani said after he attended a regional security forum in China earlier this week.
"We cannot expect it to be resolved in a few meetings.