After a difficult start to his United tenure, Van Gaal has presided over four league victories on the bounce.
United are well placed to secure a Champions league spot as they sit in fourth place with eight games remaining.
And Rooney thinks Van Gaal's competitive nature is 'incredible'.
"In terms of training sessions, every session means something," Rooney told MUTV.
"Even if it’s a little game, he wants the team who he is working with to win. He’s not happy if we don’t win. So his determination and will to win is incredible.
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Wayne Rooney loves working under Louis van Gaal
He’s not happy if we don’t win. So his determination and will to win is incredible
Wayne Rooney
"I’ve seen it in other people but more on matchday in terms of games.
"But he’s on it every day and that certainly does rub off on the players."
Rooney also thinks there is a common misperception about Van Gaal and says he has a more caring side to him.
He added: "He’s very approachable and always says to his players: ‘If you ever want to talk about anything, whether it’s about football or other things, the door is always open to you'.
"You can speak to him. He is 100 per-cent serious when it comes to training and games but, if you’re speaking to him about things other than football, he’s a genuinely nice guy."
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