Bangkok governor Chadchart Sittipunt says more than 30 shops and stalls have been selling cannabis, some openly, in the Thong Lor and Khao San night entertainment venues.
Speaking during his Facebook Live broadcast on Saturday, Mr Chadchart said he smelled cannabis while jogging past Khao San Road.
Later, he inspected the Thong Lor area and found six stalls selling unrolled cannabis flowers.
He also visited Khao San Road and found 26 shops and stalls offering cannabis for sale to customers. Two of them openly sold their products.
Public Health Minister Anutin Charnvirakul said last month that "selling cannabis flowers requires a permit and it is impossible for us to grant permits for smoking".
"Don't make people devalue cannabis," he said.
Mr Chadchart said on Saturday people should be aware of the current cannabis situation.
"We have to see how we can take care of the youngsters [against possible exposure to cannabis]," he said.
However, he insisted his exposure of cannabis sales in the two locations is not meant to be a criticism but to raise awareness among parents about the pros and cons of cannabis.
In response to the governor's live session, Mr Anutin thanked him for helping spread the word about cannabis.
Mr Anutin said people who misunderstand the liberalisation of cannabis and smoke the plant freely can face arrest.
The Public Health Ministry will intensify its campaign to educate people about cannabis, he said.
In Thailand, cannabis is now listed as a controlled herb under the Traditional Medicine Wisdom Protection and Promotion Act.
The plant was put on the list of controlled herbs in the middle of June after it was removed from the country's narcotics list to control its use.
However, a more detailed law on cannabis and hemp covering rules and regulations is still pending.