Putin met Vulin at the Eastern Economic Forum in Russia's far eastern port of Vladivostok.
Serbia, which was bombed by NATO during the 1999 war in Kosovo, has historically close ties to Russia but also aspires to join the EU.
Since Russia's full-scale invasion of Ukraine in 2022, Serbia's President Aleksandar Vucic has walked a fine line, condemning the Russian military action but refusing to join European sanctions against Moscow.
Serbia largely depends on gas supplies from Russia and its NIS oil monopoly is majority owned by Russia's Gazpromneft, although it is seeking to diversify its energy supplies.
In a statement, Vulin's office made no mention of gas supply talks but said Vulin had reassured Putin about Serbia's relationship with Russia.
"Serbia led by Aleksandar Vucic ... will never become a member of NATO, will never impose sanctions on the Russian Federation, and will never allow anti-Russian actions to be carried out from its territory," it said.
Vulin, the former head of Serbia's BIA state security agency, is under sanctions by the United States for helping Moscow in its "malign" activities, and for having links to an arms dealer and a drug trafficking ring. He resigned from the BIA when sanctions were imposed, and has denied wrongdoing.
His visit to Russia comes only days after Belgrade and France's Dassault Aviation agreed about the purchase of 12 new Rafale fighter jets for 2.7 billion euros ($2.98 billion), a move seen as a major shift away from Russia, Serbia's major weapons supplier.
