Marc Dutroux, 47, made a brief appearance behind bulletproof glass to confirm his identity in Arlon, near to where four girls went missing and two were killed.
Two of the victims were just 8 years old when they starved to death in makeshift dungeons under one of Dutroux's houses.
The prosecution claims Dutroux was helped by his wife, Michelle Martin, and two others, Michel Lelievre and Michel Nihoul, all of whom will appear in the same court later in the week.
Belgians have been outraged by the apparent incompetence of the police investigation, caused by lengthy haggling over whether Dutroux was a loner or part of a pedophilia network, Sky News said.
The unemployed former electrician also faces charges of abducting two other girls who survived.
The trial is expected to last at least two months.