Most shops have sold cigarettes to underage customers, according to Ronnachai Kongsakon, director of the Tobacco Control Research and Knowledge Management Centre at Mahidol University.
Citing research on tobacco retailing, Dr Ronnachai said 85% of convenience stores and grocery stores admit they do not check the age of customers buying cigarettes.
The findings came from a survey in 12 provinces for which 3,982 people and 1,039 store operators responded to questionnaires.
Two-thirds of shop operators said they have sold cigarettes either in packs or individually to people under the age of 20, the legal limit for cigarette purchases.
The research also found the average age of young smokers is 14.
The findings show cigarettes are easily available to youngsters and that not enough people understand the dangers of smoking.
The centre said the Public Health and Education ministries should increase efforts to educate youngsters about the harm smoking poses to themselves and the people around them, while tightening law enforcement to prevent the sale of cigarettes to underage customers.
