A Cairo misdemeanour court acquitted on Tuesday 51 from charges of illegally protesting on 25 April in downtown Cairo against a recent Egypt-Saudi deal that redrew maritime borders between the two countries.
The prosecutors had referred the defendants to court on charges of protesting without a permit as per the country's Protest Law.
The Cairo-Riyadh deal, which placed the Red Sea islands of Tiran and Sanafir in Saudi waters, has sparked widespread anger and led to several protests.
Thousands demonstrated on 15 April against the decision in what were believed to be the biggest protests by non-Islamists against President Abdel-Fattah El-Sisi since he came to office in 2014.
A second wave of the demonstrations was held on 25 April.
Tens were arrested in both sets of protests.
A controversial 2013 protest law, which bans all but police-sanctioned demonstrations, has lead to the imprisonment of hundreds of youths.
