Morocco quit the AU following a difficult debate over the status of Western Sahara according to presidents attending the summit in Addis Ababa, Ethiopia.
Morocco, which maintains that the former Spanish colony is an integral part of its Kingdom, quit the AU in 1984 after the bloc recognized the independence of Moroccan-occupied Western Sahara.
Following Monday's debate, 39 states approved Morocco's re-entry, although key members including Algeria and South Africa voted against the motion.
"Morocco is now a full member of the African Union. There was a very long debate but 39 of our 54 states approved the return of Morocco, even if the Western Sahara question remains," Senegalese President Macky Sall told media journalists.
Liberia's President Ellen Johnson Sirleaf confirmed also confirmed to the media that majority states accepted Morocco’s application to rejoin the African Union.
Sirleaf emphasized the need for African countries unity.
Morocco had been angling to rejoin the 54-nation bloc for several years and formally submitted its membership bid last year.