Egypt closed the Rafah crossing more than a year ago after Hamas took control of Gaza during fighting with the rival Fatah faction of Mahmoud Abbas, the Palestinian president.
Hamas wants Egypt to open Rafah permanently to ease an Israeli-led blockade on Gaza, but under a US-brokered accord, it cannot do so without the consent of Israel and Abbas.
Egypt said it opened the crossing as a goodwill gesture for Ramadan, which begins next week.
Sami Aby Zuhri, a Hamas spokesman, said: "The opening of Rafah for a few days will alleviate the sufferings of our people."
Ismail Haniya, the leader of Hamas in Gaza, said: "We thank [Egyptian] president Hosni Mubarak for opening the crossing today, and we hope the opening days will be extended."
Hamas wants Egypt to permanently open Rafah to ease the Israel-led blockade, but under a US-brokered agreement signed in November 2005, they cannot do so without the consent of Israel and Mahmoud Abbas, the Palestinian president.