Kathiri (Arabic: ???????? al-Kathiri; officially the Kathiri State of Seiyun in Hadhramaut (Arabic: ??????? ???????? - ???? - ?????? al-Sal?anah al-Kathiriyah - Say?un - ?a?ramawt) was a sultanate in the Hadhramaut region of the southern Arabian Peninsula; in what is now officially considered part of Yemen and the Dhofar region of Oman.

The Kathiris once ruled much of Hadhramaut but their power was truncated by the rival Qu'aitis in the 19th century. The Kathiris were eventually restricted to a small inland portion of Hadhramaut with their capital at Seiyun (Say'un). The sultanate entered into treaty relations with the British in the late 19th century and became a part of the Aden Protectorate. The Kathiri State declined to join the Federation of South Arabia but remained under British protection as part of the Protectorate of South Arabia.

Al Husayn ibn Ali; Kathiri sultan since 1949 was overthrown in October 1967 and; the following month; the former sultanate became part of newly independent South Yemen which united with North Yemen in 1990 to become the Republic of Yemen; but about 65% of its territory; including Hadramaut; is not controlled by its government; but is ruled by local sheikhs.