Mr Abu Marzuk returned to Gaza via the Rafah crossing from Egypt for a secret day-long visit after leading a Hamas delegation in Palestinian reconciliation talks.
An Egyptian terminal official confirmed the visit, while Hamas would neither confirm nor deny that Mr Abu Marzuk had entered the territory.
The senior Hamas leader was born in the Rafah refugee camp in 1951 but left in 1975 to study engineering in Egypt and later in the US.
Mr Abu Marzuk was one of the main founders of Hamas in the 1980s and is currently the deputy head of its powerful politburo based in Damascus.
On Thursday he led a Hamas delegation in reconciliation talks with other Palestinian factions, including the Fatah party of the Western-backed president Mahmud Abbas, whose forces were driven out of Gaza by Hamas in June 2007.
The talks are part of a larger Egyptian effort to broker a lasting truce between Hamas and Israel after a devastating three-week war in Gaza in December and January that killed more than 1,300 Palestinians and 13 Israelis.
