The Latics are bottom of the table and without a win in their last 10 league matches.
Sheridan, who has already enjoyed four spells as both interim and permanent Oldham boss, was sacked by League Two Notts County at the start of January with the Magpies embroiled in a relegation scrap
Oldham chairman Simon Corney said in a statement: "This is obviously a difficult decision
Stephen is a talented coach who we believed could make the transition into a successful manager
"Unfortunately things have not worked out for him or the club and we felt that a change needed to be made.
"I'd like to thank Stephen for the hard work and commitment he has shown and wish him well for the future.
"John is obviously someone we know well and we hope he can have an immediate effect on our current situation."
Source : PA
Source: PA