Convoy QS 33 was a trade convoy of merchant ships during the Second World War. It was one of the numbered QS Convoys from Québec to Sydney. The convoy was attacked in the early months of the Battle of the St. Lawrence, in the St. Lawrence River and Gulf of St. Lawrence, when German U-boats were making ad hoc forays deep into Canadian waters. The convoy was found on 6 September 1942 by U-165, which then destroyed two ships from the convoy while U-517 destroyed three.