The demilitarised zone will be secured with the help of "mobile patrol groups of Turkish contingents and contingents of Russian military police", Putin said.
For the past two years, Idlib became the shoe-box into which were pushed an estimated 20,000 opposition and rebel fighters from around the country, after their losses to regime troops and surrender deals negotiated with Russian Federation and Damascus following devastating sieges.
The United Nations has warned that a full offensive on Idlib would lead to the "worst humanitarian catastrophe in the 21st century".
Mr Putin said that the zone would be between nine and 12 miles wide between the two factions.
Neither Putin not Erdogan explained how they planned to differentiate "radically-minded" rebels from other anti-government groups.
It was not immediately clear exactly how the deal would be implemented in the province, which is home to more than 3 million Syrians and an estimated 60,000 rebel fighters from various groups.
Erdogan's call for a cease-fire in Idlib, which borders Turkey, was accepted neither by Russian Federation nor Iran at the tripartite summit in Tehran on September 7.
"The statement which we will make after the meeting in Sochi will contain new hope for the region", Erdogan said through an interpreter.
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Putin also said Russia's main worry is attacks on its military bases in Syria, which are sporadically hit by Turkey-backed rebels.
"The territory controlled by the Syrian opposition must be demilitarized and the Syrian opposition that is holding these territories will remain there".
Washington has accused the Syrian government of attacking civilians with chemical weapons in previous operations, including in Douma near the capital Damascus and in Khan Shaykhun in Idlib.
Erdoğan said Syrian Kurdish fighters in the YPG east of the Euphrates river posed the biggest threat for Syria's future.
"We are doing everything to ensure that the civilian population would not suffer", he said.
"The situation in Idlib has been quiet for two or three days".
"It looks like we obtained a result with the efforts which were made", the Turkish president told reporters on a flight back from Azerbaijan at the weekend.
Bombardment has slowed over the past week, and on Friday, Russian Foreign Minister Sergei Lavrov denied that Syrian troops were planning a major offensive on Idlib.
Rebel groups aligned with Turkey heralded the decision on Monday as a sign that the Syrian regime was hesitant to launch a full-scale ground invasion against the city and towns in this sprawling province. "But let's not create an excuse and take a step like bombing there".