Chad and Sudan have signed a deal agreeing not to host each other's rebel groups on their territory.
Rebel attacks have forced refugees to flee across borders in the region
The two countries have not resumed diplomatic relations, but have agreed to respect previous accords.
Chad cut off ties with its neighbour in April after repelling a rebel attack on the Chadian capital, N'Djamena.
The accord calls for a joint military commission to monitor the long border, but a BBC correspondent says it is not clear if rebels will be allowed home.
The BBC's Stephanie Hancock in Chad says at some 1,000km long, the border will be hard to monitor.
After the signing of the accord in N'Djamena, representatives said both countries had overcome their differences and were "turning over a new page" in their relations.
Chad hosts some 200,000 Sudanese, who fled there from the fighting in Sudan's region of Darfur over the last three and a half years.
Tensions mounted between the neighbours in late 2005 when Chad accused Sudan of arming and financing rebels in the east.
In turn, Sudan has accused Chad of supporting the Darfur rebel groups, many of whom are down from the same ethnic Zagawa group as Chad's President Idriss Deby.
An estimated 50,000 Chadians have also fled their homes near the border, AP news agency reports.