Anthony Stokes scored the only goal in the first half.
“I was delighted with the way it looked,” said Malky Mackay. “We played a very good Celtic team who are comfortable on the ball and are ahead of us in their preparations for the season.
“We had a clear chance to score and had a stonewall penalty claim turned down. There are things we will look at and work on in training, but overall this was a good workout for the players.”
Cardiff now face Bournemouth on Saturday at Dean Court, ko 1pm and then Yeovil at Husih Park next Tuesday, ko 7:45pm.
What chance of Earnie or Craig Conway playing? Both missed the Celtic game.
“We will re-assess both of them next week and they could be available for the game at Yeovil or, almost certainly, against Parma at home on Saturday week,” he said.