After a positive opening, the Sensex fell by 138.90 points, or 0.67 per cent, to 20,568.55 at 1110 hours soon after the Reserve Bank announced its third quarter policy review.
The RBI kept cash reserve ratio unchanged at 4 per cent.
The Sensex had lost over 666 points in the last two trading sessions.
Similarly, the wide-based National Stock Exchange index Nifty fell by 37.75 points, or 0.62 per cent, to 6,098.10.
The banking sector index lost the most, falling 1.63 per cent to 11,860.99, followed by FMCG index by 1.02 per cent to 6,444.40 points.