The 30-share index fell by 55.25 points, or 0.28 per cent, to 19,687.22 in early trade with shares of banking, capital goods, FMCG and realty leading the fall. Sensex had gained 9.71 points in the previous session.
Similarly, the wide-based National Stock Exchange index Nifty declined by 19.40 points, or 0.33 per cent, to 5,821.15.
Brokers said selling by funds as well as retail investors after rise in August wholesale inflation dashed hopes of RBI cutting rates later this week and a mixed trend in Asian region ahead of the US Federal Reserve's policy meeting, mainly attributed to the fall.
In the Asian region, Hong Kong's Hang Seng index fell by 5.50 points, while Japan's Nikkei Index was up by 52.32 per cent in early trade today.
The US Dow Jones Industrial Average ended 0.77 per cent higher in yesterday's trade.