Sudanese President Omar al-Bashir landed Tuesday in Juba, where he is to hold rare talks with South Sudanese President Salva Kiir, dpa reported.
The two are likely to discuss the disputed area of Abyei, laying along the countries' shared border.
The region was meant to hold a referendum on its final status, but so far no vote has been organized.
The African Union last year had proposed a referendum for this October.
The countries are also still locked in disputes over the sharing of oil revenue.
South Sudan became independent from the north in 2011, but several issues, including border demarcation, oil and economic cooperation were left open.
The two nations were pulled back from the brink of war in 2012 by international mediation efforts.