The Ramlat al-Sab'atayn () is a desert region that corresponds with the northern deserts of modern Yemen (Al-Jawf, Marib, Shabwah governorates) and southwestern Saudi Arabia (Najran province).
It comprises mainly transverse and seif dunes and covers an area of about , roughly .
The Ramlat as Sab'atayn includes part of what was known to medieval Arab geographers as the Sayhad (). It extends from al-Khawr to the edge of the Rub' al-KhÃÂlë or Empty Quarter. It includes the Yemeni muhafazahs of al-Jawf, Ma'rib and Shabwa.