Halton Regional Police Service say they received a call from hotel guests got call at about 7:35 a.m. from two people in the Staybridge Suites on Wyecroft Road.
When police and Oakville fire arrived at the scene, they detected high levels of carbon monoxide. Two people were treated for carbon monoxide poisoning and taken to hospital, according to officials.
Police and fire are searching for the origin of the leak.
The hotel has been evacuated in its entirety. Oakville Transit has sent buses to transpor evacuated guests and staff to the Halton Regional Centre.
The hotel is near Bronte Road and Highway 403.