Checkpoint police opted to search the Bangkok taxi when it arrived on Phuket about 7pm last night. Tachatchai lies at the northern approach by road to Phuket.
One gram of marijuana - enough for what marijuana smokers call a ''joint'' - was found in the shoulderbag of a man police named as Daniel Paul Beilken, 22.
It is believed Mr Beilken and his friend, also Australian, were planning to catch a flight from Thailand within days.
Police say Mr Beilken is likely to be granted bail when he appears in court on Monday, but he is not likely to be permitted to leave Thailand until his case has been resolved.
The latest arrest comes as police and local authorities this week announced a campaign to make people aware of the extent of drug addiction on Phuket in advance of a visit by Deputy Prime Minister Chalerm Yoobamrung on February 17.
Khun Chalerm will speak at an anti-drugs rally at Saphan Hin public park in Phuket City that is expected to attract 12,000 people.
Thailand's ''no tolerance'' policy on drugs is certain to be strictly enforced on Phuket in advance of the rally, with drug-test raids likely on venues and in homes in areas where drug-taking is rife.
A planning meeting at Provincial Hall in Phuket City this week heard that in the October-December quarter of 2011, there were 329 arrests for offences involving marijuana on Phuket.
There were 19 arrests involving possession or sale of heroin and 13 involving cocaine in the same period, the meeting was told.
Methamphetamines were far more significant among the 3666 arrests for drugs in that period, police said. A total of 777 offenders were arrested and 7852 grams of crytal meth (yah ice) seized, along with 2095 arrests and 180,692 tablets involving ya bah, Phuket's illegal drugs of choice.
The visit by the Deputy Prime Minister is part of a nationwide campaign to highlight the dangers of drug addiction. Phuket has 3486 registered addicts.
More than 80 percent of the inmates at Phuket's overcrowded Provincial Prison in Phuket City are serving sentences or awaiting trial over drugs.