The Commerce Ministry will probably call bids each week to sell rice including 5% white rice for exports in a move aimed at unloading its huge stockpile.
But the sales will be considered carefully to avoid an impact on local prices, said Manat Soiploy, director-general of the Foreign Trade Department.
"We've been authorised by the government to gradually sell rice for local consumption and exports until the end of this year," he said.
This week, the ministry organised bids to sell 586,000 tonnes of rice, mainly fragrant rice, for domestic consumption.
Mr Manat said nine bidders offered satisfactory prices close to those in the previous bids of between 29,800 and 30,000 baht a tonne. The winners will be announced on Monday.
Rice companies joining the bidding were Asia Golden Rice, Capital Rice, Chia Meng, CP Intertrade, Olarn Thailand and Sothorn Intertrade.
Meanwhile, the Thai Rice Exporters Association (TREA) reported the country exported 4.47 million tonnes in the first eight months of this year for 93.9 billion baht, a 45% and 33% year-on-year decline in volume and value, respectively.
However, export prices jumped by 18% to an average of US$676 a tonne.
Nigeria remains the top buyer, ordering 865,543 tonnes from January-August, followed by Iraq at 447,579 tonnes and Indonesia at 303,640 tonnes.
South Africa also imported 239,423 tonnes and the US 227,084 tonnes.
The TREA said the market was active last month after speculation that Nigeria may raise its import levy to 113% by year-end from 53%.
The rumours have prompted large imports, with traders rushing to place orders ahead of the deadline.
Nigeria bought 43,200 tonnes rice last month after 4.72 tonnes in July.
India and Vietnam sell their white rice at $435-465 a tonne compared with $577 a tonne by Thailand.
The TREA estimates exports will total 500,000 tonnes this month thanks to shipments to Japan and Iraq.
The US, Canada, Ivory Coast and Ghana could be strong buyers this year, helping the Thailand to meet its shipment goal of 500,000 tonnes a month, said the TREA.