The verdict in the case, which has been closely followed by human rights campaigners, was delivered at dawn by the Court of Appeals in Sale near Rabat, the official news agency MAP reported.
Morocco and the Algeria-backed Polisario Front independence movement have accused each other of provoking the deadly clashes between police and Sahrawi protesters at a camp for displaced people in Gdeim Izik in November 2010.
In 2013 a military court sentenced the 25 defendants to jail terms ranging from 20 years to life imprisonment.
Morocco says Western Sahara, a former Spanish colony mostly controlled by Rabat, is an integral part of the kingdom.
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The Polisario Front demands a referendum on self- determination for the territory.
Amnesty International and Human Rights Watch this week issued a joint plea for the Moroccan authorities to ensure the verdict in the trial was not based on confessions or statements "obtained under torture or other ill-treatment during police interrogations".
The NGO Action by Christians for the Abolition of Torture has criticised what it called an "unfair trial" that took into account "confessions signed under torture".
The Moroccan authorities have sought to underline what they called the "transparency" and "fairness" of the civil trial, which was open to the press and international observers.
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