The Head Coach, who joined in January 2019, took the club to the National League South title last season.
But their return has not lived up to expectation - they sit second from bottom of the table and haven’t picked up a point since November.
The Stones hope a change can provoke a response and push them clear of an instant return to Step 2.
Former club captain George Elokobi will be in caretaker charge until a replacement is found.
He will look after the team for Sunday’s FA Trophy match away to Notts County, the club have announced.
Chief executive Bill Williams said: “We have made the difficult decision to part company with Hakan and his assistant Terry Harris, following the recent run of results.
“These decisions are never easy, and the Board felt the time was right to make this change now – with just under half the season remaining – to give us an opportunity to retain our National League status.
“On behalf of the owners, directors and all staff involved with Maidstone United, we would like to express our thanks to Hak and Terry for all their time, effort and guidance while they’ve been at the club.”