The victim, a 27-year-old resident of the northern province of Nihn Binh, entered a Hanoi hospital on February 12, and died on Thursday night.
Earlier this week, a 40 year-old man from the northern province of Hai Duong, 50 km (31 miles) southeast of Hanoi, died after six days of treatment for severe pneumonia and multiple organ failure.
All three of the deaths are thought to have been caused by the victims eating infected chicken meat.
Vietnam ranks second after Indonesia in bird flu fatalities, with an overall death toll of 50 since the lethal H5N1 virus was first reported in the country in 2003. The two main sources of infection are the country's northern Thai Nguyen and central Quang Binh provinces.
According to the World Health Organization, avian influenza has so far killed 227 people in 360 confirmed cases worldwide. Although there have been no incidences of human to human infection, experts fear that it may mutate into a form that could easily be transmitted from person to person, causing a global pandemic.