The Magpies sit 10th in npower League One, but lost to rock-bottom Hartlepool on Saturday and have won just two of their last 11 games in all competitions.
Chairman Ray Trew: "This obviously is not a decision that we have taken lightly and certainly not one that I have taken any pleasure in reaching, I have a tremendous amount of respect for Keith Curle both as a man and a manager.
"Since Keith first came in, just under a year ago, we, as a board, have backed him to bring in the players that he felt could move Notts County onto the next level and felt that he assembled a squad capable of challenging for promotion this season.
"However, recent displays have unfortunately not lived up to expectations and our poor disciplinary record this season has only further hampered our progress.
"Attendances at Meadow Lane have dropped in recent weeks and this has made this a business decision as much as a footballing one, because fans are obviously key to the club and their support is essential.
"I would like to thank Keith, as well as Colin Lee and Colin West, for all of their hard work and effort over the past year, there have been plenty of highs to enjoy in that time but there comes a time when we, as a board, have to consider what we feel is best for the future of the club."
Source: Manchester City MAD