Members of all Palestinian movements attended the demonstration which began at the Al-Omari Mosque in Gaza City after Friday Prayers and ended at the headquarters of the Red Cross.
Demonstrators chanted slogans such as "We are all Khader Adnan" to express their support for the hunger striker.
"The Palestinian people, with all its components and its factions, will never abandon the hero prisoners, especially those who lead this hunger strike struggle," said Hamas Prime Minister Ismail Haniyeh, who participated in the demonstration in Gaza.
"In his hunger strike, Khader Adnan is not fighting for a personal cause, but for the defense of thousands of prisoners," said Nafez Azzam, a Gaza leader of the Islamic Jihad Movement in Palestine.
Meanwhile, hundreds of Palestinians also demonstrated in the northern West Bank city of Jenin, while Palestinian officials said many other prisoners in Israeli jails had started hunger strikes in support of Adnan.
Thirty-three-year-old Khader Adnan is being held without charge or trial in what Israel calls “administrative detention.”
The prisoner started the open-ended hunger strike a day after his arrest 64 days ago to protest against his detention as a violation of his basic rights and to highlight abuse and humiliating treatment during his arrest and interrogation.
According to a medical report issued on Thursday, he is "in immediate danger of death.”
Last week, an Israeli military court rejected an appeal against the detention, stating that Adnan had to remain in jail until May 8, 2012.
He was reportedly beaten by Israeli forces and sustained injuries when they raided his home outside the city of Jenin in the north of the occupied West Bank.
According to Palestinian Central Bureau of Statistics and prisoner advocacy groups, there are currently over 6,000 Palestinian prisoners, including legislators, in Israeli jails, many of whom have been rounded up without charge or trial. Independent sources put the number of the inmates at 11,000.