A Cairo appeals court on Tuesday acquitted 51 people who were handed two-year sentences last month for attempting protests without a permit against the handover of two Red Sea islands to Saudi Arabia.
The verdict can be appealed by the prosecution before a higher court.
The protests on April 25 against the handover of the Red Sea islands of Tiran and Sanafir to Saudi Arabia were largely foiled by a heavy police deployment and a campaign of arrests in preceding days.
Protests have been all but banned in Egypt under a law passed months after President Abdel-Fattah al-Sissi, then head of the armed forces, ousted Islamist president Mohammed Morsi in 2013.
Authorities were roiled by demonstrations on April 15 against the handover of the islands, which had been quietly announced during a visit to Cairo by Saudi King Salman.
The protests, centred around the Journalists Syndicate building in central Cairo, were among the largest non-Islamist demonstrations against al-Sissi's administration in two years.
The controversy has led to a renewed crackdown on dissent, with prominent rights lawyer Malek Adly, members of a performance group who satirized the handover agreement, and two journalists all now behind bars.
The Egyptian government says that technical work by experts from both countries established that the islands of Tiran and Sanafir were in fact Saudi territory.
However, opposition activists accused the authorities of "selling" the islands in compensation for billions of dollars of Saudi aid and financing to Egypt since the ouster of Morsi.
An administrative court is due to rule on June 21 in a case taken by rights lawyers who argue that the agreement under which the islands will be transferred to Saudi Arabia is unconstitutional.
On May 15, another court sentenced 101 alleged demonstrators to five years in jail over the April 25 protests. The 47 defendants in the case who were held in custody appealed and their sentences were reduced to a 100,000 pound (11,258 dollar) fine each.
The total amount of 4.7 million pounds for those fines was collected by activists within 10 days, local news site Mada Masr reported.