The 30-share index, which had lost 43.09 points in the previous session, fell further by 39.47 points, or 0.19 per cent, to 20,815.45, led by losses in stocks of banking, oil and gas, auto and FMCG sectors.
Similarly, the wide-based National Stock Exchange index Nifty declined by 13.75 points, or 0.22 per cent, to 6,188.10.
Brokers said sustained selling by funds amid a weak trend in the Asian region following overnight weakness at the US market mainly influenced the trading sentiment.