Gross domestic product (GDP) grew 3.3 percent during the April to June period from the previous quarter, when the economy had expanded 11 percent, according to the National Economic and Social Development Board (NESDB).
GDP rose 4.2 percent in the latest quarter compared with a year earlier.
The Thai economy has rebounded sharply after suffering a double-digit contraction in the wake of the kingdom's worst floods in decades.
"The main drivers were increases in private consumption as well as investment in industry zones hit by severe flooding last year," NESDB secretary-general Arkom Termpitayapaisit told reporters.
Household consumption rose strongly as the government's economic stimulus measures lifted spending on durable goods such as cars, the board said.
The months-long floods last year killed hundreds of people and caused widespread damage to Thailand's industrial heartland north of Bangkok.
At their height the floodwaters affected 65 of the country's 77 provinces, deluging hundreds of thousands of homes and disrupting global supply chains.
The NESDB forecasts economic growth of 5.5-6.0 percent for the whole of 2012.