Indonesia's benchmark index fell below the psychological level of 2,000 Monday in tandem with declines in Asian markets.
The Jakarta Stock Exchange Composite index closed 20.509 points or 1 percent lower to 1,999.167 even though gainers led losers 115 to 82 with 48 stocks unchanged.
Traders also attributed the fall to plan for massive demonstration Tuesday in the Indonesian capital on Labor Day.
Among top decliners were heavyweight Telkom which slid 2.3 percent after reporting a 12-percent fall on year of first-quarters net profit, and Bank Rakyat which dropped 2.8 percent on lower first-quarters earnings.
The local currency, the rupiah, also fall as players reduce U.S. dollar shorts on weaker emerging market currencies driving the greenback to close at 9,080 rupiah, up from Friday's 9,060.