About 7,000 people and Communist Party officials in Ili prefecture attended the "mass gathering for public sentencing, public arrests and public criminal detention, punishing a group of violent terrorist criminals in accordance with the law", said an online report by the official news agency Xinhua.
Judicial officials at the stadium issued punishments for crimes including murder, separatism and organising, leading or participating in a terrorist group, harbouring criminals and rape.
Three were sentenced to death for using hatchets and other weapons to murder a family of four last year "using extremely cruel methods", the report said.
At the stadium, police also announced the formal arrests of 38 suspects and detained another 27.
Photos showed armed officers guarding the premises, and the accused crammed into backs of lorries wearing orange vests and bent forward as helmeted security forces stood over them.
The event was intended to demonstrate authorities' "resolute determination crack down on the 'three forces' of violent terrorism", Ili's deputy party chief was cited as saying, referring to separatism, extremism and terrorism.
China used mass trials in the 1980s and 90s to try to combat the rise in crime driven by the social upheavals that accompanied the country's dramatic Reform and Opening economic overhaul, but the practice later faded.
Beijing at the weekend vowed a year-long crackdown on terrorism following a string of attacks blamed on militants from Xinjiang, home to the mainly Muslim Uighur minority, with violence in recent months increasingly targeting civilians and spreading elsewhere in China.
Last week five suspects killed 39 people and wounded more than 90 at a market in the regional capital Urumqi.
On April 30, the final day of a visit by President Xi Jinping to the region, attackers killed one person and wounded 79 at an Urumqi railway station.
In March knifemen killed 29 people and wounded 143 at a railway station in the southwestern city of Kunming, an incident dubbed "China's 9/11" by state media.
Beijing says it faces a violent separatist movement driven by religious extremism and backed by overseas terrorist organisations.
But experts question how organised the groups in Xinjiang are, while rights groups point to cultural repression of Uighurs and economic favouritism towards an influx of the ethnic majority Han into the resource-rich region.
Dilshat Rexit, a spokesman for the exiled World Uyghur Congress, said in a statement: "The judiciary has become a means of assisting China's crackdown against Uighurs.
"China's provocations will spur even more despairing Uighurs to fiercer resistance."