Moussa reached the Palestinian side of the Rafah crossing shortly before 10:00am (0700 GMT) where he was welcomed by members of Gaza's ruling Hamas movement, as well as representatives of various Palestinian groups.
He crossed into the enclave from Egypt, two weeks after Israel's deadly interception of a Gaza aid flotilla that was intended to deliver humanitarian aid to the territory.
At a joint news conference with Moussa shortly after his arrival, Basim Naeem, the Hamas health minister, said the visit indicated that "the boycott between Gaza and the Arab nation was broken".
Egypt had kept its border with Gaza largely closed, bolstering Israel's embargo, since Hamas seized control of the Strip from Palestinian president Mahmoud Abbas's Fatah forces in 2007.
But Cairo eased restrictions at its Rafah crossing with the territory after Israeli marines killed nine pro-Palestinian Turkish activists during violent confrontations on the Turkish-flagged aid convoy on May 31.
Palestinian and Arab League officials said Moussa's visit was also aimed at giving momentum to reconciliation talks between Hamas and Fatah. Egypt has sponsored the talks but they have failed to bridge deep mistrust between the two rivals.
Moussa, however, said he had not come to Gaza to give support to any political faction, but to meet the Palestinian people of the territory.
Ismail Haniya, Hamas's leader in Gaza, said he hoped that Moussa's visit would result in practical measures to end the siege on Gaza.