The Republican presidential debate on CNN Wednesday night drew 22.939 million total viewers according to Nielsen, CNN said.
The debate was the network's highest-rated program ever, topping an episode of Larry King Live with Ross Perot and Al Gore in 1993.
A Republican debate on Fox News Channel on August 6 drew 24 million viewers, the most in cable news history and the biggest non-sports number ever for cable.
The presence of businessman and reality TV star Donald Trump has boosted the ratings for political coverage.
In the early debate involving secondary candidates, CNN averaged 6.3 million viewers.
CNN said that it also had 4.5 million live video streams during the debate. Usage peaked at 9:45 p.m. with 921,000 streams going at the same time.