5 years for insulting ruler
The court gave Kuwaiti Mohammad Eid al-Ajmi the maximum sentence for the comments, news websites al-Rai and alaan.cc reported.
In recent months Kuwait has penalised several Twitter users for criticising the emir, who is described as "immune and inviolable" in the constitution.
"We call on the government to expand freedoms and adhere to the international (human rights) conventions it has signed," said lawyer Mohammad al-Humaidi, director of the Kuwait Society for Human Rights, commenting on the case.
Courts in Kuwait generally do not comment to the media.
Amnesty International said in November Kuwait had increased restrictions on freedom of expression and assembly.
It urged Kuwait to ensure protection for users of social media, whether they supported or opposed the government, as long as they did not incite racial hatred or violence.
Kuwait, a U.S. ally and major oil producer, has been taking a firmer line on politically sensitive comments aired on the internet. Twitter is extremely popular in the country of 3.7 million.
In January, a court sentenced two men in separate cases to jail time for insulting the emir on Twitter.
In June 2012, a man was sentenced to 10 years in prison after he was convicted of endangering state security by insulting the Prophet Mohammad and the Sunni Muslim rulers of Saudi Arabia and Bahrain on social media.
Two months later, authorities detained Sheikh Meshaal al-Malik Al-Sabah, a member of the ruling family, over remarks on Twitter in which he accused authorities of corruption and called for political reform.
The recent Twitter cases have been carried out under the state security law and penal code. Last year Kuwait passed new legislation aimed at regulating social media.
Public demonstrations and debates about local issues are common in a state that allows the most dissent in the Gulf, but Kuwait has avoided the kind of mass unrest that unseated four heads of Arab states in 2011.
But tensions intensified between authorities and opposition groups last year ahead of a parliamentary election deemed unfair by opposition politicians and activists.
The opposition movement said new voting rules introduced by Sheikh Sabah by emergency decree in October would skew the December 1 election in favour of pro-government candidates. The emir said the old voting system was flawed and that his changes were constitutional and necessary for Kuwait's "security and stability".