Centre-back Adam Lockwood will take interim charge of the Lions who were felled 3-2 at Solihull Moors on Saturday, despite leading 2-1 with 13 minutes remaining.
The club are bottom of National League, with the Lions back in action on Saturday at home to fifth-bottom Bromley.
A statement released on the club’s website on Sunday afternoon read: “Following the run of poor results since the start of the season, the Board of Guiseley AFC have made the decision to part company with manager Mark Bower and his assistant Danny Boshell.
“The current run of five successive defeats sees the club struggling at the foot of the National League table and the board felt that a change was necessary to address the position.
“Centre-back Adam Lockwood has agreed to take interim charge of the team and he will take training on Tuesday evening. Adam will remain in charge until a permanent replacement is appointed and he will be considered along with all other applicants for the job.
“Martin Stringfellow and Steve Dickinson will continue their roles as part of the backroom staff.
“The club wishes to place on record its thanks to Mark and Danny for their efforts over the last three years, during which time promotion to the National League has seen the club operating at its highest ever level.
“The club wishes Mark and Danny all the best for the future.”