As of 0145 GMT, the main TAIEX index was down 60.50 points at 8,929.76, after closing up 0.26 percent on Wednesday.
Losses were broad-based with the electronics subindex down 0.7 percent and the financials off 0.8 percent.
Among the actively traded counters, technology firm AU Optronics Corp was down 1.5 percent and Innolux Corp was lower 1.1 percent.
China Development Financial Holding Corp was 0.9 percent lower and CTBC Financial Holding Co Ltd was down 0.3 percent.
The Taiwan dollar was up T$0.056 at T$30.436 to the US dollar