The 40-year-old former Scotland international has been under pressure at Boundary Park for some time following poor form, but earned a stay of execution after masterminding a famous FA Cup victory over Liverpool last weekend.
However, eight defeats out of nine games in League One has left the Latics hovering above the relegation zone and Dickov has decided to quit after two and a half years in the job.
A statement on the club's official website read: "After yesterday's defeat to Walsall, Paul Dickov has decided that for the good of Oldham Athletic Football Club, it is best that he steps aside."
Oldham chairman Simon Corney spoke with Dickov this morning, and before those talks opened said he and the manager would "need to get a plan together and work something out, and figure out whether or not together we can handle this".
Speaking on BBC Radio 5 Live's Sportsweek programme, Corney expressed sympathy for Dickov.
He said: "It is not down to a lack of hard work - he has been working very hard and I think the players have to shoulder a huge amount of responsibility.
"I have been at too many games now where we just haven't performed. When they put in a performance like they did against Liverpool, you know they have the talent and ability, and yet in the day-to-day bread and butter games, they are not showing what they need to show week in and week out.
"I feel for Paul, I really do, because he trains them hard, he works hard and does a lot of things to prepare the team, and once they cross that line, what can he do?
"It is a horrible situation. I'd like to think I will never have another manager who is a friend of mine again, because it is horrible."