The worst ethnic unrest in decades began July 5 when minority Uighurs attacked Han, who make up China's dominant ethnicity, only to face retaliatory attacks two days later.
Many Uighurs, who are a Turkic Muslim ethnic group linguistically and culturally distinct from the Han, resent Beijing's heavy-handed rule in Xinjiang, their traditional homeland.
Four months later, Xinjiang remains smothered in heavy security, with Internet access cut and international direct dialing calls blocked.
The official China News Service reported that the nine were executed after a final review of the verdicts by the Supreme People's Court as required by law, but gave no specific date or other details. Earlier reports had identified those condemned as eight Uighurs and one Han.
The timing of the executions was not especially fast for China, which puts more people to death than any other country.
Politically sensitive cases are often decided in weeks, especially when they involve major unrest.
The nine had been convicted of murder and other crimes committed during the riots in Urumqi, Xinjiang's capital.
China blames the rioting on overseas-based groups agitating for broader rights for Uighurs in Xinjiang.
The news service said another 20 people were indicted on Monday on charges related to the deaths of 18 people and other crimes committed during the riots. All but two of the prisoners listed in the report had Uighur sounding names, with the others appearing to be Han.
Overseas Uighur activist Dilxat Raxit condemned the executions as motivated by politics and the need to appease Urumqi's angry Han residents, who marched in the thousands through the city in September to demand trials of those responsible for the July violence and the perpetrators of a bizarre series of hypodermic needle attacks.
"We don't think they got a fair trial, and we believe this was a political verdict," said Raxit, who serves as spokesman for the Germany-based World Uyghur Congress.
"The United States and the European Union did not put any pressure on China or seek to intervene and for that we are extremely disappointed," he said.