The champions head off to the Nou Camp eight points adrift of their arch-rivals after a wobbly start to the league campaign in which they have lost twice, the same number of games they lost over the whole of last season.
"I have confidence in my players, as always," Mourinho said.
"When they work hard obviously I have more confidence in them, complete confidence."
Mourinho was highly critical of the attitude of his players after their defeats at Getafe and Sevilla, but they have responded since then winning four matches on the trot in all competitions, netting 14 goals.
"I think you can see the players have understood they had to change," he said.
"They understood they had to be more motivated, to be more focused and that the way the team was, would have led to a negative end to the season.
"It's a credit to them. They have changed, and in this way it is easier for good things to happen."
There has been a steady stream of media stories about rifts within the dressing room over the last month, with time on the substitutes' bench for Spain defender Sergio Ramos and Germany midfielder Mesut Ozil being reported as some kind of 'punishment'.
In response, Mourinho said the decisions were all part of the normal routine of a team.
"There is no need for drama when a player is on the bench," he said. "There are 24 in the squad so that means there are 13 who don't play, and every time there is someone on the bench there is a furore.
"I am paid to decide on the line-ups, I try to do it to the best of my abilities. Full-stop."
A defeat would leave Real 11 points behind a Barca side who dropped only 15 and 18 points respectively during their title winning campaigns in 2009-10 and 2010-11. Real dropped only 14 themselves last season.
"All I am looking for is continuity more than the result," the former Chelsea and Inter Milan boss said.
"I am worried about the way we play, the ambition, the commitment, the team performance and good individual performances.
"We need to get back to the level of last season, as you know it is difficult to maintain for months on end. We lost that level of play, and all I am worried about is recovering it, as we have been doing, and this game is important in this sense."