The Edmonton refinery, which celebrated its 60th anniversary of operations in 2011, is designed to process 142,000 barrels of oil sands per day into light oils. Suncor said the planned maintenance was completed on time.
"The impact of this maintenance on refinery throughput and utilization has been factored into Suncor's annual guidance," it added in its Monday statement.
About 1,400 employees were put to work for the Edmonton refinery overhaul.
The company said it completed maintenance at its smaller Montreal facility last week.
Suncor operates three refineries in Canada and one in the United States with a combined processing capacity of 462,000 bpd.