Mustafa Barghuti, a Palestinian parliamentarian who was on board the boat, said arrival in Gaza marked "an historic day in the life of the Palestinian people."
"We have arrived here without having to apply for permission from the Israelis," he said.
"Today the embargo has been broken. It is a message to the people of Gaza that we have not been abandoned"
Mustafa Barghuti, Palestinian parliamentarian
"Today the embargo has been broken. It is a message to the people of Gaza that we have not been abandoned."
Gaza's 1.5 million Palestinians have been living under a crippling Israeli blockade since Hamas took full control of the territory after pushing out security forces loyal to Mahmoud Abbas, the Palestinian president, in June 2007.
Since then there have been shortages of basic necessities such as food, fuel and medicines as Israel has strictly controlled all deliveries.
Last week the International Committee of the Red Cross said virtually no medical supplies were reaching the Gaza Strip.
It blamed a lack of cooperation between Palestinian authorities in the West Bank, where Mahmoud Abbas, the Palestinian president who heads the Fatah movement holds sway, and Hamas, which took control of the Gaza Strip last year.
"We got a list of zero stock medicines in Gaza, like baby formula, paracetamol, anti-histamine tablets," said Ibrahim Hamami, a Palestinian Briton who is a family physician.
Israel pulled troops and settlers from the Gaza Strip in 2005 but still patrols its waters, tightening overland border restrictions after Hamas took over.
In August, 46 activists made a similar sea voyage to the Gaza Strip without interference from Israeli authorities.
Organisers have said that they hope to make the trips into a monthly exercise in order to provide regular relief to Gaza.
Supporters say their next goal is to break the Israeli blockade by air, by landing an aid aircraft in Gaza.