The Sensex today opened 55 points lower as funds and retail investors preferred to book profits after yesterday's rally.The 30-share index, which had gained 173 points in the previous to 17,559 points. Banking, metal and IT stocks came under selling pressure and were trading in the negative territory with moderate losses.The wide-based National Stock Exchange index Nifty fell by 21.20 to 5,267.85 points.Meanwhile, Hong Kong's Hang Seng index shed 0.90 per cent, while Japanese Nikkei fell by 0.18 per cent in morning trade.