Intra-day profit booking in realty, metal and power stocks pushed the index into a negative zone to touch a day's low of 15,136.
The Sensex finally ended (provisional) with a loss of 77 points at 15,173.
The market breadth was marginally positive - out of 2,675 stocks traded, 1,413 advanced, 1,179 declined and 83 were unchanged today.
The NSE Nifty ended (provisional) with a loss of 22 points at 4,517.