The newly-promoted club have only won once in the league this term, and a total of seven points has left them in 19th position in the table entering the international break.
Following Saturday's 1-0 home defeat to Alaves, the powers that be have relieved Martin, who was in his third stint as manager of the Spanish club, of his duties.
"After the meeting this afternoon of the board and the sporting management of Osasuna, the club has decided to relieve from office the coach Enrique Martin," read a club statement.
"After analysing the sporting situation of the team, the club has identified the need to make this decision with the aim of reversing the current dynamics.
"Osasuna would like to thank the effort and dedication of Enrique Martin, whose name will go down in history thanks to his brilliant contribution as a player and coach. The club wishes you the best of luck in your future professional challenges."
Martin, 60, made over 250 league appearances as a player for Osasuna and has also previously coached their B team.