Naw Kham of Myanmar, Hsang Kham of Thailand, Zha Xika of Laos, and Yi Lai, who is stateless, were executed by lethal injection in Kunming, Yunnan province.
Chinese Internet users have criticized the televised procession to the execution site as insensitive, the BBC reported.
Naw 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's gang was accused of attacking two Chinese cargo ships in October 2011, killing 13 Chinese sailors. The gang also was accused of being involved in a kidnapping-for-ransom case targeting Chinese citizens on the Mekong.
Official Chinese media reported a joint police operation by China, Laos, Myanmar and Thailand led to the gang members' arrest last year.
Naw and five accomplices were convicted of intentional homicide, drug trafficking, kidnapping and hijacking in December.
Five of the men were sentenced to death, though one man was given a reprieve. The sixth suspect was given an eight-year prison term.