JOIN USThe Committee to Protect Journalists (CPJ) said Iran and China led the list, each with 34 imprisoned journalists.
Together, they accounted for nearly half of the world's total.
Eritrea, Myanmar and Uzbekistan filled out the remaining roles of the five worst jailers among 28 nations currently imprisoning journalists.
"The increase in the number of journalists jailed around the world is a shocking development," said CPJ executive director Joel Simon.
Iranian detainees range from high-profile writers such as Issa Saharkhiz, a well-known state journalist who started writing reformist columns, to Navid Mohebbi, a women's rights blogger who, at age 18, was the youngest in the CPJ study of jailed journalists.
China in 2009 had jailed 24 journalists. This year's increase to 34 included Uighur and Tibetan journalists who have covered regional unrest. Among the detainees were a Tibetan writer known as Buddha, who wrote about economic disparities between Tibet and the rest of China, and Gheyrat Niyaz, an Uighur website editor who covered ethnic violence in Xinjiang Uighur Autonomous Region.