At 12.30pm, the key index was down 3.67 points to 1,581.23.
The decline was led by glove makers, which had come under pressure following a rally last week.
Top Glove shaved 12 sen to RM6.59 for a third straight day of losses, Hartalega lost 10 sen to RM13.26 and Supermax fell 11 sen to RM6.68.
Pantation plays aso came under pressure. Sime Darby Plantations dropped seven sen to RM4.90, IOI dropped give sen to RM4.24 and Kuala Lumpur Kepong slid 46 sen to RM23.34.
However, it was a good day for energy counters as rising crude oil prices lifted the earnings outlook.
Hengyuan Refining Corp rose three sen to RM5.57, Hibiscus Petroleum added two sen to 60 sen, Dialog rose five sen to RM3.10 and Dayang gained two sen to RM1.17.
Of actives, Nestle was down 80 sen to RM13720, BAT shed 10 sen to RM13.04 and Carlsberg slid six sen to RM22.14.
Meanwhile, Asian markets were bullish on the back of Wall Street's extended rebound and progress in vaccine distribution.
Japan's Nikkei rose 1.4% while South Korea's Kospi added 0.25%.
China's composite index and Hong Kong's Hang Seng added 0.5% apiece. Australia's ASX200 jumped 1.1%.