Thai Finance Minister Pridiyathorn Devakula has resigned, citing media pressure and rifts in the government.
Mr Pridiyathorn has angered foreign investors
Mr Pridiyathorn, who was appointed after last September's coup, has been under growing pressure in recent weeks.
He has been criticised for a number of policy decisions, including a move to tighten foreign business laws.
His departure from the increasingly troubled government comes just a week after that of another senior economic adviser, Somkid Jatusripitak.
In a news conference on Wednesday morning, Mr Pridiyathorn said he no longer wanted "to work under the influence of some people whose behaviour is not entirely transparent".
"Hiring individual(s) from the previous government... is a weak excuse," he told reporters - a reference to Mr Somkid, a senior official in the previous administration who was hired by Mr Surayud on 15 February but resigned after less than a week following sharp criticism.
In the days following last September's coup, Pridiyathorn Devakula's name was at the top of many people's list of possible prime ministers.
He was a respected central bank governor during the time of the previous administration, and was courted by the leaders who ousted former Prime Minister Thaksin Shinawatra.
In the end he settled for the position of finance minister, as well as becoming one of the deputy prime ministers, and both appointments were widely welcomed in Thailand and abroad.
But according to the BBC correspondent in Bangkok, Jonathan Head, his credibility has suffered after two bungled policy initiatives - both of which were poorly explained and spooked foreign investors.
Mr Pridiyathorn faced huge criticism after imposing capital controls in late December, which triggered a 15% plunge in the stock market, forcing the authorities to reverse some of the measures.
Investors also criticised a move in January to tighten rules for foreign companies that operate in Thailand.
Mr Pridiyathorn's relationship with Prime Minister Surayud Chulanont has also deteriorated, culminating in Mr Surayud's short-lived attempt earlier this month to appoint Mr Somkid.
Unpopular though he was with foreign investors, Mr Pridiyathorn's resignation may only cause further damage to the interim government's standing at home, our correspondent says.
The government is now being widely criticised for a lack of clear leadership and internal disarray.
Little progress has been made in bringing charges of corruption against the previous administration.
And many politicians are worried that the military generals who launched the coup may start to reconsider their promise to return Thailand to full democracy by the end of the year.