Barca have picked up just 15 points from 10 games in La Liga and have already lost twice in the group stage of this season's Champions League.
They are ninth in the table, six points adrift of the joint leaders after losing at Rayo Vallecano on Wednesday.
The loss was Barca's third in their last four games and it followed defeat in Sunday's Clasico to Real Madrid.Â
In a statement, the Spanish club said: "The president of the club, Joan Laporta, informed him [Koeman] of the decision after the defeat against Rayo Vallecano.
"Ronald Koeman will say goodbye to the squad on Thursday."
The former Netherlands, Everton and Southampton boss, 58, could only guide the five-time European champions to third place in the league last season.
Â
Â
Â
Â
Â
Â