There are plans to remove them from the enclosure that has been their home for ages into a riverside reserve on the edge of the city.
"There are worse bear pits, but the bears are confined - they look up and can see only the sky," said a Swiss Animal Protection society spokesman.
Funding has yet to be confirmed, but the reserve could be built by 2007.
The design for the 10,000 square-metre park would allow the bears to live outside 24 hours a day.
At the moment, they are locked up at night.
They would be able to hibernate in caves, dig the ground and catch fish.
Bears were first brought to the city in 1513 and their image features on its flag.