Victoria police say they received an alarm call indicating a break and enter at the church just before 10 p.m. Saturday night. Several officers and a K9 team searched the building but did not locate any suspects.
Police say officers found a display case inside the cathedral had been smashed and several items were stolen, including artifacts from the 17th century.
The missing items include: two gold and silver chalices, Canadian coins, a small communion plate and a mote spoon.
Logan McMenamie, dean of the Cathedral, told CBC News he believes the thieves hid in the church before it was locked up for the night.
Police are analyzing the scene for forensic evidence and are also asking the public to be on the lookout for any of the stolen items.