The Sensex fell by nearly 150 points in opening trade today on selling by funds ahead of the RBI monetary policy amid weak trend on Asian bourses. The 30-share index of the BSE that gained 191 points in the previous session fell by 150 points to 18,209 points with banking, auto, realty and IT stocks leading the fall. In a similar fashion, the broad-based National Stock Exchange index Nifty lost 57 points to 5,454 points in the first few minutes of the trade.