The New York-based media watchdog group, in its annual census of imprisoned journalists, said that as of December 1, a total of 125 journalists were behind bars, two fewer than at the same point in 2007.
It said 56 of the imprisoned journalists were considered online journalists -- bloggers, Web-based reporters, or online editors -- surpassing the number of print journalists for the first time.
Print reporters, editors, and photographers are the next largest category of jailed journalists, with 53 cases, the CPJ said, adding that television and radio journalists and documentary filmmakers constitute the rest.
For the 10th consecutive year, China was the leading jailer of journalists, the CPJ said, followed by Cuba, Myanmar, Eritrea and Uzbekistan.
It said 24 of the 28 jailed journalists in China worked online including Hu Jia, a prominent human rights activist and blogger serving a three-and-a-half year prison term.
Cuba holds 21 writers and editors in prison, the CPJ said, while Myanmar is detaining 14 journalists including five arrested while trying to spread news about Cyclone Nargis.
There are 13 journalists in prisons in Eritrea, the CPJ said, and the Eritrean authorities "have refused to disclose the whereabouts, legal status, or health of any of the journalists they have imprisoned."
Six journalists are being detained in Uzbekistan, the CPJ said, including Dzhamshid Karimov, a nephew of the country's president who was a reporter for independent news websites.
"Online journalism has changed the media landscape and the way we communicate with each other," said CPJ executive director Joel Simon.
"But the power and influence of this new generation of online journalists has captured the attention of repressive governments around the world, and they have accelerated their counterattack.
"The future of journalism is online and we are now in a battle with the enemies of press freedom who are using imprisonment to define the limits of public discourse," he said.
The CPJ noted that 45 of the imprisoned journalists are freelancers, most of them working online, who "often do not have the legal resources or political connections that might help them gain their freedom."
The CPJ, in the report available at cpj.org, said anti-state allegations such as subversion, divulging state secrets, and acting against national interests were the most common charges used to imprison journalists.
Other countries on the list besides the top five are: Afghanistan (1), Armenia (1), Azerbaijan (5), Bangladesh (1), Burundi (1), Cameroon (2), Democratic Republic of Congo (2), Ecuador (1), Egypt (1), Ethiopia (2), Gambia (1), Iran (5), Iraq (1, in US custody), Iraq (1, in Iraqi Kurdistan custody), Israel and the Occupied Palestinian Territories (4), Ivory Coast (1), Maldives (1), Peru (2), the Philippines (1), Russia (2), Senegal (1), Singapore (1), Sri Lanka (3) and Vietnam (2).