The Sensex resumed higher at 27,919.45 and firmed up further to an all-time high of 28,027.96 on initial strong buying on the back of strong foreign capital inflows into equity market coupled with higher Asian cues.
However, it failed to maintain this level and declined afterwards to 27,818.23, showing a loss of 50.40 points, or 0.18 per cent at 1100 hours.
The CNX 50-share Nifty also moved down by 16.25 points, or 0.19 per cent, to 8,320.75 after hitting life-time high of 8,383.05.
Meanwhile, foreign portfolio investors (FPIs) bought shares worth a net Rs 2,537.13 crore, according to provisional data from the stock exchanges.