Howard announced the decision in a statement to USA Today on Friday.
"As I continue to embark on my NBA journey, I have decided to sever my relationship with Dan Fegan and Relativity Sports," Howard said in the statement. "I have the utmost respect for Dan, but this is the right decision for me. My sole focus remains working with my teammates to position the Rockets for a pursuit of a championship. I wish Dan and the team at Relativity all the best in the future."
Howard, 30, is expected to opt out of his contract after the season and having different representation might help him on the free-agent front. He hasn't yet selected a new agent.
Fegan has a reputation of being hard to deal with while working on deals for his clients. He has recently been fired by both Los Angeles Clippers center DeAndre Jordan and Washington Wizards point guard John Wall.
The Rockets did shop Howard leading up to last week's trading deadline and isn't know whether or not the inability to make a deal has anything to do with Howard's decision to fire Fegan.
Howard is completing the third season for a four-year, $88 million contract.