Peter Efferso, 46, was nabbed at Immigration before he could board a TUI Nordic weekly charter flight from Phuket to Copenhagen.
The drugs have a street value of about three million baht.
''He appeared to be nervous so immigration officers decided on further questioning,'' Phuketwan was told. ''The man had no luggage, just a carry-on bag.''
Heroin is not the drug of preference in Thailand where methamphetamines are more frequently trafficked.
But Efferso, who arrived on Phuket on December 9 and was granted a 30-day tourist visa, now faces a long stint in a Thai jail if convicted.
Police Lieutenant Colonel Watcharin Jiratthikanwiwat of Tachatchai Police Station said an investigation into the background of the Danish man had begun.
''He said he had been staying in Patong [a popular destination on Phuket's west coast] but so far we have been unable to find his name recorded at any resort there.''
The flight was due to take off at 8.30am and Mr Efferso was arrested about 6.30am as he began the process of passing through Immigration.
Drugs have been detected hidden in the luggage of inbound passengers at Phuket airport but it's unusual for a traveller to be arrested for carrying drugs out of Phuket, although there are many cases where passengers from Thailand have been arrested on arrival in neighboring countries.