Image technology company Agfa-Gevaert and zinc producer Nyrstar will exit, the exchange said in a statement.
At the same time the weightings of the Bel20 basket will change, for example cutting GDF Suez by half and more than doubling the representation of Fortis
The changes will take place on March 2 after trading hours.
Membership on the Bel-20 is based on minimum levels of the market capitalisation of the free float and the volume of trade.
Befimmo shares dropped a relatively modest 8.2 percent last year, while Telenet's went down by 38.3 percent. Agfa stock plummeted 82.3 percent and that of Nyrstar 86.7 percent.
The Bel-20 index fell by 53.8 percent in 2008.
(Reporting by Philip Blenkinsop; Editing by Hans Peters) Keywords: BELGIUM/BEL20 (email@example.com; +32 2 287 6838; Reuters messaging: firstname.lastname@example.org) COPYRIGHT Copyright Thomson Reuters 2009. All rights reserved. The copying, republication or redistribution of Reuters News Content, including by framing or similar means, is expressly prohibited without the prior written consent of Thomson Reuters.