The girl lived in Prey Lvea commune, Prey Kabass district in Takeo province. She developed symptoms of fever, cough, and vomiting on January 25 and was admitted to the Kantha Bopha Hospital on January 31 when her condition had worsened.
"Unfortunately, despite intensive medical care, she died yesterday, said a joint statement.
"There is evidence of recent deaths among poultry in her village and the girl has history of coming into contact with poultry prior to becoming sick," it said.
Cambodia first reported H5N1 in poultry in January 2004. To date, the country has recorded 27 human cases of the virus, killing 24 people.
Minister of Health Mam Bunheng said bird flu is still a threat to the health of Cambodians and children still seem to be most vulnerable.
"I urge parents and guardians to keep their children away from sick or dead poultry," he said. "If their kids have fast or difficulty breathing, they should be brought to medical attention at the nearest health facilities."
The statement said that globally, since 2003, there have been 616 laboratory confirmed cases of the H5N1 virus with 365 related deaths.