Open interest for the March contract fell to 178 contracts from 210.
Brokers said prices could move in a narrow range over the next few days, backed by the high physical price of Thai five percent white rice at 10.60 baht per kg.
It was only 8.5-8.6 baht per kg a year ago.
Brokers said they expected support at 10.44-10.66 baht per kg and resistance at 10.62-10.65 baht per kg.
"The local price is expected to stay steady despite weak overseas demand, supported by thin local supply," said one broker.
Investors were keeping a close eye on a new cabinet line-up, especially the new commerce minister, brokers said.
"We are waiting to see what the new commerce minister would do with its stock and its buying scheme," said one.
Prices would be put under pressure if the government decided to release its stock, estimated at 3 million tonnes, brokers said.
The government has said it wants to buy 9 million tonnes of paddy by the end of March when its intervention scheme is due to finish.
Brokers said they expect the government to extend the buying scheme to support the price of a second small crop, due to arrive on the market in early April.
It was not immediately known if the government's decision on Monday to cut its diesel subsidy by 0.60 per litre, which will affect farmers, had any impact on physical rice prices.
Thailand, the world's largest rice exporter, started rice futures trading on August 26.