Alberta Health Services said the man died on Sunday night, two days after accidentally receiving chemicals while undergoing dialysis.
It's not yet known if his death is connected to the contamination of the dialysis line.
The man's age or where he is from is not being released.
One patient remains in hospital and two have been discharged. All are being monitored closely by Alberta Health Services.
"This was an extremely unfortunate incident, and our thoughts are with the families and loved ones of all four patients impacted," Vickie Kaminski, AHS President and CEO, said on Tuesday.
Kaminski said the incident happened Friday when a routine line flush was being done. She said the wrong valve was opened and instead of peracetic acid and hydrogen peroxide being flushed out of the system it went into the line that was circulating through the dialysis equipment.
"It is human error that was at the root cause of this," said Kaminski, adding that no other patients are at risk.
The mistake was noticed within minutes of happening, said Kaminski and the water supply was immediately turned off.
On Sunday, health officials said the four patients affected by the incident were in stable condition.
The long-term health effects on the patients who received the wrong dialysis isn't yet clear.
"When we did the research, it said it causes a sunburn like reaction inside the body," said Kaminski.
"We are taking this incident extremely seriously," she said, adding the incident will be reviewed by AHS.