Offloading long positions from operators in view of expiry of July-contract on Thursday, weak global cues, continuing geo-political tensions also affected the sentiment.
Weakness in the rupee against the dollar, as the domestic unit touched 61-mark after three months, was also the factor behind fall in share values.
Shares of capital goods, refinery, metal, power, realty, PSU, consumer durables, IT, auto and banking declined sharply on heavy selling pressure.
"The overall sentiment also remained downbeat after India's fiscal deficit crossed half the budget estimate in the first three months of the fiscal," said Jayant Manglik, President-retail distribution, Religare Securities.
The Sensex resumed higher at 26,173.47 and moved up to 26,181.83 but declined afterwards to 25,459.13 before ending at 25,480.84, showing a loss of 645.91 points or 2.47 pct.
It had gained by 1,102.40 points or 4.41 per cent in the previous two weeks.
The NSE 50-share Nifty also fell by 187.85 points or 2.41 per cent to 7,602.60.
