Describing the report as "inaccurate and inconsistent", the foreign ministry said Forbes magazine had wrongly attributed assets to the King that were not part of his personal fortune.
Forbes' royal rich list of the 15 wealthiest monarchs was released on Thursday and placed 80-year-old King Bhumibol top with an estimated personal fortune of 35 billion dollars.
"The Crown Property Bureau has clarified that the report is inaccurate and inconsistent," the foreign ministry said in a statement.
"Forbes has included land and other assets belonging to the Crown Property Bureau, which is not in His Majesty's personal net worth," it said.
Bangkok also said that the magazine's reference to the king's alleged role in the military coup of September 2006 was "incorrect".
Bhumibol, the longest-serving head of state with 62 years on the throne, had played "no role", it said, in the coup that deposed prime minister Thaksin Shinawatra, who now seeks political asylum in Britain.
The foreign ministry explained in a rare clarification by the government of the monarch's role that the king had acted in strict accordance with his constitutional role in giving his assent to the military's takeover.
Forbes published its list of wealthy monarchy noting that because most royals inherit their wealth, share it with extended families or keep it "in trust for their nation", none would qualify for the magazine's famous annual world wealth ranking.