The four former guards stood trial for dereliction of duty at Longjiang County People's Court in the city of Qiqihaer this morning.
The jail terms for the four ranged from one-year-and-four months to two-and-a-half years.
The prisoner, Wang Dong, who has been lodged in Nehe Prison since December 2012 after being convicted of kidnapping, contacted several women near the prison through messaging app WeChat using a smartphone given to him by a prison guard.
The blackmail came to light when one of Wang' victims reported that she was being blackmailed to the police in late 2014.
Wang Dong was fined 220,000 yuan (USD 33,900) and given 13 years and nine months jail, including the time remaining under his original sentence for kidnapping, by Nehe City People's Court in July.