Four empty tanker cars that had previously been used to haul jet fuel jumped the tracks just before 7 a.m. near the Bramalea GO station near Steeles Avenue East and Dixie Road.
The derailment caused major delays on GO Transit's Kitchener Line.
Police shut down a section of Steeles Avenue to traffic until inspectors determined there was no risk to the public.
A message posted on GO Transit's website said they've been advised by CN rail traffic control that the affected tracks will be back in service before the evening commute.
"At this time we do not anticipate an impact to service," the statement read.