Gross domestic product in the third quarter was lower than the 2.47 percent forecast in August, and was up just 0.09 percent from the previous quarter, according to preliminary figures from the Directorate General of Budget, Accounting and Statistics.
The economy grew 2.49 percent year-on-year in the second quarter.
The agency blamed weaker than expected exports, consumer spending and corporate investment.
Exports account for about two-thirds of GDP. They fell 7.0 percent in September from a year earlier to $25.3 billion on falling demand from most markets including China and the United States, according to the finance ministry.
The government in August revised its full-year growth forecast downwards to 2.31 percent, citing a weaker global economic outlook as well as slowing exports and private consumption in the second half.
Taiwan's trade-reliant economy has been hit by ongoing weakness in the global economy, with Europe battling a long-running debt crisis and China seeing a slowdown in growth momentum.
Last year the island's economy grew 1.32 percent, its slowest pace in three years.