A Thai court on Friday acquitted a man held for nearly a year under controversial royal defamation laws after his own brother accused him of insulting the king in their home.

The unusual case raised concerns among rights activists that a suspect could be held without bail for so long under the lese majeste rules, on the basis of one person's allegations of remarks made in private.

Bangkok's Criminal Court dismissed the case against Yuthapoom Martnok, 36, who was accused of defaming the king while watching television at home in 2009, his lawyer Saovalux Pongam said.

"The judge said the brother had serious conflicts with the defendant, therefore the court must treat the plaintiff's testimony cautiously," Saovalux added.

The defendant's wife Jongkol Khongtin, 36, said the two brothers had a history of feuding.

"Most of the time they barely talked to each other because they do not get along," she told AFP after the verdict.

Yuthapoom -- who denied the charges -- had been held in the Bangkok Remand Prison since September 2012. Several requests for bail were denied.

"He should have been granted bail to fight the case. Putting him in jail for 11 months is like diminishing his rights as a being human," Jongkol said, adding that she was now struggling with debts.

Jongkol said she hoped lese majeste allegations would be examined more carefully in the future before a suspect is indicted.

The royal family is a highly sensitive subject in politically turbulent Thailand and King Bhumibol Adulyadej, 85, is revered by many Thais. He has suffered from a range of ailments in recent years.

Thai courts have handed down a series of tough sentences for insulting the monarchy in recent times, to the dismay of human rights campaigners.

Under the legislation, anyone convicted of insulting the Thai king, queen, heir or regent faces up to 15 years in prison on each count.

Critics say the lese majeste law has been politicised, noting that many of those charged are linked to the Red Shirt political movement, which is broadly loyal to ousted premier Thaksin Shinawatra.

Thailand has been riven by political divisions since Thaksin was overthrown by royalist generals in a coup in 2006.

Two months of mass street protests by the Red Shirts in early 2010 triggered the kingdom's worst civil violence in decades with 90 people killed.