Exports dropped for a third straight month in January, falling a more-than-expected 5.6% from a year earlier, the Commerce Ministry said on Friday.
Analysts in a Reuters poll had predicted a 1% slip in exports, a key growth driver.
In December, shipments contracted 1.7% from a year earlier.
The decline in customs-cleared exports in January was due to falling shipments of rice, electronics, gold and cars, the ministry said.
Exports to the US rose 8.3% in January from a year earlier but shipments to China slumped 16.7%.
The strong baht, Asia's best-performing currency this year, has increasingly hurt exports, particularly rice orders, a ministry official said.
In January, imports surprisingly jumped 14% from a year earlier, after sliding 8.1% in December. The poll forecast was for a 1% decline in January. Officials said the import surge was due to shipments of arms and military weapons for drills.
For January, there was a trade deficit of $4 billion, compared with a forecast of a $320-million surplus, and December's $1.06 billion surplus.
The ministry has forecast export growth of 8% this year after a 6.7% increase in 2018.