A rescue basket was deployed to free the passengers from cars about 10 metres above the ground, Bangkok Post online said, adding that no one was injured.
A preliminary investigation showed that a brake problem caused it to stop unexpectedly.
The monorail, which was pressed into service in late 2007, can transport between 50 and 70 passengers at a time in air-conditioned cars.
The nationalities of the foreigners were not announced.