The 30-share index fell by 156.98 points, or 0.79 per cent, to 19,840.11 in early trade with shares of Infosys, Reliance Industries and ICICI Bank leading the fall. Sensex had rallied over 1,757 points in the previous four sessions.
Similarly, the wide-based National Stock Exchange index Nifty declined by 42.85 points, or 0.73 per cent, to 5,853.90.
Brokers said emergence of profit-booking by funds as well as retail investors at prevailing higher levels amid a mixed trend in Asian region mainly attributed fall in stock prices.
In the Asian region, Hong Kong's Hang Seng index fell by 0.38 per cent, while Japan's Nikkei Index was up by 0.62 per cent in early trade.