The 30-share index shed 36 points, or 0.17 per cent, to 20,213.26 with shares of banking, power, FMCG, PSUs and refinery sectors succumbing to profit-booking.
BSE Sensex had gained 354.16 points in the previous two sessions.
Similarly, the NSE Nifty dipped below 6,000 mark by falling 8.70 points, or 0.14 per cent, to 5,998.75.
Brokers said selling by funds as well as retail investors after two sessions of gains and a mixed trend in Asian region, as traders nervously await signs of progress in solving a budget stand-off in Washington, mainly attributed to the fall.
In the Asian region, Hong Kong's Hang Seng index fell by 0.83 per cent, while Japan's Nikkei Index was up by 0.81 per cent in early trade today.
The US Dow Jones Industrial Average ended 0.18 per cent higher in yesterday's trade.