"The internal crisis in Syria cannot be solved through the deployment of such weapons," Mr Larijani, who is close to the Islamic Republic's supreme leader, said at a news conference in Beirut where he went after leaving Syria.
Turkey's request earlier this week followed several incidents in which violence has spilled across the border from the civil war in Syria, with mortar rounds falling a short distance inside. Patriots would be useful in intercepting ballistic missiles - a much more serious but still hypothetical threat. Nato has said it will consider the request "without delay".
The Syrian foreign ministry also criticised the Turkish move, calling it "a new provocative step".
Mr Larijani, who met Syrian president Bashar Assad in Damascus, said Iran was seeking a peaceful solution to the war in Syria.
"The difference between us and the others when it comes to Syria is that the others want to impose democracy through weapons," he said. "Iran cannot accept or support such a way. I don't think democracy can be achieved through rocket-propelled grenades."
Iran is Assad's strongest ally in the region, and anti-government activists accuse Tehran of sending both weapons and fighters to Syria.
Syria's conflict erupted in March 2011 with an uprising against Assad's regime, inspired by other Arab Spring revolts, but quickly morphed into a civil war that has since killed more than 40,000 people, according to activists.
In violence around Syria on Friday, Islamic extremists battled with pro-government Kurdish gunmen in the northern town of Ras al-Ayan near the border with Turkey, activists said.