Thousands of people took to the streets of the Armenian capital, Yerevan, on Thursday demanding the resignation of Prime Minister Nikol Pashinyan.
His government announced last month it would cede several uninhabited border villages to its neighbour and long-time rival Azerbaijan.
The move is seen as an important milestone on the road to peace between the countries which have fought two wars since the collapse of the Soviet Union.
But the decision has angered many, with opposition politicians accusing the prime minister of giving up territory with no guarantees.
The protesters had walked about 160 kilometres from the villages to the capital where they gathered in Republic Square, waving Armenian flags and chanting slogans.
Archbishop Bagrat Galstanyan, a senior Armenian cleric and a leading figure of the protests, addressed the crowd, shouting "a new vision, new narrative, new parade, new victory".
In April, Armenia said it would return border villages to Azerbaijan after its rival waged a military campaign in Nagorno Karabakh, a majority ethnic Armenian region inside Azerbaijan.
The decision caused tens of thousands of people to stream into Armenia, sparking demonstrations and calls for Pashinyan to resign.
