Erdogan's talks with Serbian President Aleksandar Vucic focused on trade and investment, but also covered political relations in the region, where many countries have historic and religious links with Turkey from centuries of Ottoman rule.
Erdogan said that the current trade exchange between the two countries of USD 800 million (682 million euros) "is not enough" and that it should rapidly grow in the near future.
He promised more Turkish investments, including into a highway linking the Serbian and Bosnian capitals.
Relations between Serbia and Turkey have improved recent years, after decades of mistrust between the two nations.
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Serbia was ruled for almost 500 years by the Ottoman Empire.
Turkey backed Bosnian Muslims in the 1990s war that pitted them against the Christian Orthodox Serbs and Catholic Croats.
"This is not 1389, but 2017," Vucic said, referring to the year when the Ottoman occupation of Serbia started.
"Today, Serbia considers Turkey as its friend." Serbian and Turkish officials signed several agreements today, including an amended free trade accord that will open the Turkish market to several Serb products.