Firefighters responded at approximately 4:30 a.m. on Sunday to a call from a house in the 1200 block of Avenue D North.
They found the occupants outside and could see flames through the front window when they arrived, according to a statement.
A fire battalion chief told Global News crews fought the blaze for about two hours.
Neither civilians nor firefighters were injured in the fire.
While the investigation into the fire continues, Saskatoon fire is estimating about $100,000 in damages.