The woman died of the H10N8 strain in the southeastern city of Nanchang on December 6, the Jiangxi provincial health department said in a statement on its website.
Biologists say the strain has never been detected in humans before.
Bird flu infections raise fears that a virus could mutate to become easily transmissible, potentially triggering a pandemic.
An outbreak of H7N9 bird flu has infected at least 139 people on the mainland and resulted in 45 deaths, but fatalities have dropped significantly since the end of June.
Other cases of H7N9 infection were also reported in Hong Kong and Taiwan.
The woman in Nanchang was admitted to hospital on November 30 with severe pneumonia and died of respiratory failure and shock, the provincial health department's statement said.
She had visited a local live poultry market before succumbing to the virus, it added.
People who have been in close contact with the woman have not shown any signs of illness so far, it said.
Local health officials also cited unnamed experts as saying initial assessments suggested the death was an individual case and the risk of the virus spreading between humans was low.
The H10N8 bird flu strain has never been detected in humans before, University of Hong Kong microbiologist Yuen Kwok-yung told Hong Kong Cable TV on Tuesday.
In August scientists reported the first likely case of direct person-to-person transmission of H7N9.
But they told people not to panic, describing the virus's transmissibility as "limited and non-sustainable".