The six men are alleged to have joined a terrorist network based in Britain and the Afghanistan-Pakistan border region.
Khaled ben Mustapha, Mourad Benchellali, Nizar Sassi, Imad Achab-Kanouni and Redouane Khalid declined to comment on the charges on arrival at the main criminal court in Paris. A sixth man, Brahim Yadel, is in custody.
All six have spent lengthy periods in detention in Cuba and France. They face up to 10 years in prison if convicted of the terrorism charges.
Presiding trial judge Jean-Claude Kross said the six men, aged 24 to 38, were captured in Afghanistan as they tried to escape the advancing US forces and their Afghan allies.
Some were handed over by villagers for a reward of up to 5,000 euros ($6,399).
Pakistani forces later transferred them to the US military, which moved them to Guantanamo Bay, on suspicion they had been fighting for Afghanistan's Taliban government.
The Frenchmen were held without charge or trial with hundreds of other "enemy combatants." They have complained of insults, physical and psychological torture, and deprivation of food and water.
The six men complain of torture
and insults at Guantanamo Bay
Prosecutors say that five of the six men trained at al-Qaeda camps in Afghanistan from 2000 to 2001 and that Kanouni received fundamentalist religious training there.
Prosecutors have highlighted that the father and brother of one of the accused, Mourad Benchellali, were convicted last month of planning attacks in France in 2002.
Benchellali has admitted to attending a training camp in Afghanistan, but said friends dragged him into it. "For two months, I was there, trapped in the middle of the desert by fear and my own stupidity," he wrote in the International Herald Tribune last month.
The verdict is expected in mid-July.
The trial follows a ruling by the US Supreme Court on Thursday which stated that military tribunals created by George Bush to deal with Guanatanamo detainees were unlawful and violated the Geneva Conventions.