"The Annan mission, perhaps, is the last chance for Syria to avoid a long period civil war," Medvedev told the visiting Annan, the UN-Arab envoy on the Syrian crisis, here, reported Xinhua.
The Russian president also said that Moscow will offer its help to resolve the Syrian conflict in a peaceful way.
Medvedev hailed the former UN secretary-general's peacemaking efforts.
"We very much appreciate your intermediary efforts in solving Syrian problems," the president said, expecting such efforts would bring "positive results."
During the meeting, Annan said he would make all endeavours to ensure access to humanitarian aid for strife-torn Syria.
He appreciated Russia's involvement in the Syrian issue and support for his mission.
"Hopefully, we will manage to make a positive contribution to the resolution of the Syrian issue with Russia's most active involvement," Annan said.
The meeting was held at the governmental airport, Vnukovo-2, before Medvedev's departure for a nuclear summit in Seoul and a BRICS summit in New Delhi.
Earlier Sunday, Annan also held a meeting with Russian Foreign Minister Sergei Lavrov in a closed format.
According to a Russian Foreign Ministry's statement, when meeting with Annan, Lavrov called on to end violence in Syria and establish a Syrian political process.
The Russian minister also urged the international community to provide consolidated assistance to Annan's mission, the ministry said.
Annan arrived in Moscow Saturday.