Officials on Saturday said the latest victim in Thailand was admitted to hospital on 29 January after having contacted the virus from infected chickens.
"The boy, Eakathan Pongkhan, died at 6.50 pm," a nurse at the Chaiyaphum Hospital said.
Thailand had earlier said it aimed to conquer bird flu by the end of the month.
Meanwhile, China reported four new confirmed outbreaks and United Nations agencies warned the disease could take years to eradicate in Vietnam, the worst hit country with 14 deaths.
The outbreak of the H5N1 strain of the bird flu has led Vietnam to cull 35 million chickens and inflicted devastating losses on local poultry farmers.
But the World Health Organisation (WHO) and the Food and Agriculture Organisation (FAO) both said hopes for a quick recovery of Vietnam's poultry industry were premature.
"We believe the outbreak wont be eradicated for several months, probably years," WHO spokeswoman Maria Cheng said.
"We are right now only starting the engine to control the outbreak. It will be long." FAO official Anton Rychener said.
The FAO estimates some 80 million chickens and other fowl have now been culled to contain the disease, various strains of which have struck 10 Asian nations and the United States.