The trial is taking place in the North Caucasus District Military Court in the city of Rostov-na-Donu.
The defendants are accused of organizing a suicide car bombing at a central market in the North Ossetian capital, Vladikavkaz, in September 2010 that killed 20 people and injured 240.
Prosecutors also say the defendants conducted several deadly attacks against local officials and law enforcement officers in neighboring Ingushetia.
Russia's mostly Muslim-populated and ethnically mixed North Caucasus region has been volatile for years.
Militants frequently attack police and local officials, saying they are fighting to create an Islamic state in southern Russia.