Activists have condemned the Kuwaiti Court of Appeals' decision to uphold a 10-year prison sentence for a blogger.
Hamad al-Naqi was convicted last year of insulting the Prophet Muhammad and the kings of Saudi Arabia and Bahrain on Twitter, among other charges.
Monday's ruling showed "just how little Kuwait respects freedom of expression", Human Rights Watch said.
The New York-based group called on the authorities to quash the verdict and release Mr Naqi immediately.
There has been a political crisis in Kuwait since June 2012, when the Constitutional Court declared as illegal elections to the National Assembly that saw the Islamist-led opposition made significant gains.
Since then, prosecutors have charged dozens of politicians, online activists and journalists with "offending the emir", Kuwait's head of state.
Mr Naqi - a Shia Muslim - was found guilty by a lower court in June 2012 of insulting the Sunni kings of Saudi Arabia and Bahrain, provoking sectarian tensions, insulting the Prophet Muhammad and the prophet's wife Aisha and his companions, mocking Islam, and misusing his mobile phone to disseminate objectionable comments.
The 23-year-old pleaded not guilty to all the charges, arguing that someone had hacked his Twitter account and impersonated him.
"Punishing Hamad al-Naqi for criticising neighbouring monarchs clearly violates international rights standards," said Joe Stork, deputy Middle East director at Human Rights Watch. "It's disappointing that on appeal the authorities didn't try to remedy this violation."
"Locking up critics isn't going to make Kuwait's political crisis go away."
Mr Naqi can still appeal against the verdict at the Supreme Court.