Nearly 700 ducks and young chicken were culled to contain the outbreaks in northern Thai Nguyen province and the southern Mekong delta province of Dong Thap, the national animal health department said in an online report.
Vietnam has now reported recent bird flu outbreaks in four of its 64 provinces and municipalities, including northwestern Dien Bien province near the Lao border as well as Cao Bang near China.
Four people have died of bird flu this year in Vietnam, bringing the human death toll to 46 since the virus broke out here in late 2003.
Communist Vietnam, once the nation worst hit by the killer virus, contained earlier outbreaks through mass vaccination campaigns, the culling of millions of poultry and public education initiatives.
The virus resurfaced earlier this year, especially among waterfowl, hitting scores of poultry farms in an outbreak that at its peak in May spread to 18 provinces and municipalities.
To contain the virus, more than 163 million head of poultry have been vaccinated since the beginning of the year.
Globally, the World Health Organisation had recorded 322 cases of bird flu in humans, 195 of which were fatal.
Experts fear the virus could mutate and become easily transmissible between humans, leading to a pandemic with the potential to kill millions.