The bizarre accident occurred shortly before 10.30am when a 20-year-old man driving the tractor applied the brakes on a road in La Tour-de-Trême, losing control of the vehicle and its load, cantonal police said.
The tractor and tank toppled onto the sidewalk and struck the woman, who was pedalling in the opposite direction.
The cyclist was killed on impact, police said.
The tractor driver, travelling from the town of Bulle to Intyamon, slowed down either because of traffic or possibly because of a pedestrian, according to a statement issued by the cantonal force.
Police have issued an appeal for witnesses to the incident, which took place on the Rue de l’Ancien Comté in the heart of La Tour-de-Trême, a scenic village in the Gruyère region.
The home town of the victim was not disclosed.
An investigation into the case continues.
Anyone with information about the accident is asked to contact Fribourg police in Vaulruz or by phone on 026 305 67 40.