The provincial higher people's court in Kunming, capital of Yunnan province, rejected appeals from those convicted in last year's deaths of Chinese sailors, the official Xinhua News Agency reported.
Death sentences were confirmed for Naw Kham, accused of being a Myanmar drug lord, and three of his lieutenants. The court also upheld the death sentence with a reprieve for one suspect and an eight-year prison term for another.
All six had been convicted of intentional homicide, drug trafficking, kidnapping and hijacking by a local court in Kunming, Xinhua reported.
Naw Kham was accused of being the head of the largest armed drug-trafficking gang on the Mekong River, which flows through China, Laos, Myanmar, Thailand, Cambodia and Vietnam.
Naw Kham's gang was found to have attacked two Chinese cargo ships in October 2011, killing 13 Chinese sailors died, the report said. The gang also was accused of being involved in a kidnapping-for-ransom case targeting Chinese citizens on the Mekong.
A joint police operation by China, Laos, Myanmar and Thailand led to the gang members' arrest early this year, the report said.
Xinhua said Naw Kham's lawyer had pleaded for a reduced sentence.
The higher court cited the "severe outcome" of the crimes in rejecting the appeals.
The death sentences of the four will be submitted to the Supreme People's Court in Beijing for review prior to the executions, Xinhua said.