The MacTier Subdivision is a major rail line in Ontario, Canada, which is owned and operated by the Canadian Pacific Kansas City.

The line stretches 126.9 mi (204.2 km) from Toronto in the south to MacTier in northern Muskoka.

[1] The MacTier Subdivision is the easternmost section of CPKC's present-day transcontinental route and is the railway's only connection between its eastern and western holdings which is fully within Canada.

Between 1955 and 1978 the MacTier Subdivision hosted CPR's premier transcontinental passenger train, the Canadian, from Toronto to Vancouver.

Operation of the Canadian was transferred to Via Rail in 1978, which switched over to CNR's Newmarket Subdivision, rejoining the former CPR route at Parry Sound, 23 mi (37 km) north of MacTier.