Liu Han, his brother Liu Wei and three accomplices appealed to the high court in the central province of Hubei after they were condemned to death in May for "organising and leading a mafia-style group", murder and other crimes.
The court rejected the appeal, it said in a posting on China's Twitter-like Sina Weibo.
"The crimes of organising and leading a mafia-style group and murder Liu Han and Liu Wei committed were extremely serious and a punishment should be meted out to several offences combined," it said.
Liu Han led private company Hanlong, which is based in the southwestern province of Sichuan and once launched a billion-dollar bid for an Australian firm.
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Sichuan is one of the power bases of Zhou, who once enjoyed vast power as China's security chief but was announced last week to be under investigation for corruption.
The influential business magazine Caixin has reported that Liu Han once had dealings with a businessman believed to be Zhou's son. State media have also hinted that the gang had connections to central government officials.