The new figures bring to six the total number of deaths from this summer's outbreak in the city. Another 65 people have are reported to have contracted the illness.
The Legionnaires' disease is caused by bacteria accumulating in stagnant water, including air-cooling systems.
Over the past few days, a cleanup and inspection operation has been underway, but officials have not been able to pinpoint the source of the outbreak.
Authorities say the outbreak is focused in the Saint-Sauveur neighbourhood.
On Wednesday, Solange Allen, a woman whose husband passed away from the disease over the weekend, said health officials didn't do enough to warn citizens of the outbreak.
The symptoms are similar to those of the flu, including coughs, fever and chills.
The disease is not contagious and cannot be transmitted from one person to another. It presents little or no risk to most people, although elderly people are more vulnerable.
Earlier this month, Doctor François Desbiens from the Quebec Public Health Agency said finding the original water source is often difficult.
"We know from previous eclosions in the United States and Europe that, with the wind, the droplets can go as far as one kilometre away from the building they are coming from."
In early August, the agency sent 2,500 notices to the owners of all large buildings within a 1.5-kilometre area to clean their cooling systems.
According to reports, Quebec City Mayor Régis Labeaume has cut his vacation short to return to the city and deal with the outbreak.
He has scheduled a news conference for Friday morning.