The main TAIEX index slipped to 8,619.83 as of 0200 GMT, extending the 1 percent fall on Friday.
The benchmark index has lost about 4 percent so far this month, triggered by foreign selling. (For a table of foreign trading, double click )
Most sectors were traded in the negative territory, with the food sub-index plunging nearly 5 percent. Electronics shares slid 0.3 percent, while banks rose 0.4 percent.
The Taiwan dollar was up by 0.069 percent to stand at T$30.392 to the US dollar.