A seventh person was sentenced to life in prison, the Xinhua news agency said.
The riots in July were prompted by long-simmering resentment between minority Uyghurs and majority Han Chinese.
The Uyghurs are mostly Muslims in western China's Xinjiang province. Some Islamists refer to the region as East Turkistan.
Last month, China sent 7,000 officials to Urumqi to ease tensions after Han Chinese protested a series of attacks in which syringes were used as weapons.
The syringe attacks by Uyghurs started August 17.