Veteran striker Dean Windass showed the home forwards the way when he reacted sharply to ram home a loose ball for the only goal of the game in the 52nd minute.
On this display City boss Dave Jones will be very busy wheeling and dealing in the summer.
The Bluebirds showed changes from the side beaten at QPR, with skipper Darren Purse, Darcy Blake and Warren Feeney all starting.
Steven Thompson had a glorious chance to give the Bluebirds the lead in the ninth minute when he met a pinpoint cross from Peter Whittingham, but his header went tamely to Hull keeper Boaz Myhill. Two minutes later he nodded a Joe Ledley cross straight at the keeper.
Roger Johnson thundered in a 30-yard strike that Myhill pushed to safety and then a Whittingham try midway through the half beat the visitors' keeper, but went well wide of the post.
The Tigers almost made Cardiff pay in the 38th minute when Windass turned sharply before rattling in a shot that David Forde did well to kick over.
The Bluebirds forced a couple of corners at the start of the second half but were unable to open up the visitors' defence.
Hull took the lead six minutes into the second half when the Cardiff defence failed to clear. Stephen McPhee lashed in a shot that Forde could only parry and Windass was first to react and fire into the back of the net.
With two minutes of normal time remaining Aaron Ramsey made his debut for Cardiff to become the youngest player at 16 years and 123 days to play a senior match for the club.
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