The group operated in the southern province of Guangdong via overseas gambling websites between March 2008 and April 2013, using the sites to lure bettors and take commissions, the official Xinhua news agency said.
"Of those convicted, 55 were found guilty of opening online casinos, seven guilty of gambling and six guilty of both crimes," Xinhua said, citing a court in the provincial capital, Guangzhou.
Prosecutors said the ring was run within a circle of friends and relatives like a pyramid scheme, Xinhua reported. They were given sentences between one year and five months and nine years, and ordered to pay fines up to 20 million yuan ($3.2 million).
Gambling has been illegal on mainland China since 1949, though a state lottery does operate.
Underground rings have drawn gamblers in increasing numbers in recent years, Xinhua said.
The southern Chinese territory of Macau, a special administrative region, runs a string of legal casinos. Two horse racing tracks operate in nearby Hong Kong.- Reuters