The Hoops boss is planning to pair Caulker up with recent signing Rio Ferdinand after having a bid in the region of £8m accepted, Sky Sports News reports.
"We've agreed a fee for Steven Caulker, who I like very much," said Redknapp. "I had him at Tottenham as a player and he's done very well. I think for him to come and play with Rio would be a great experience for him.
"I think for Steven Caulker to come in and be part of it with those experienced players will be great for him."
Cardiff paid Spurs more than £8m for Caulker last summer, a record fee for the Welsh club at the time.