In the 1987 national elections, the Communist Party of Belgium (PCB-KPB) lost all parliamentary representation for the first time since 1925.This failure reflects the accelerated collapse of Belgian Communism in just a decade. The events of 1989 and 1991 in Central and Eastern Europe and in the USSR will then confirm the de facto disappearance of the PCB-KPB. The article goes back to the roots of the decline of a medium-size Communist Party, but showed political and social relevance from 1925 to 1985.The decline is due to the industrial and socio-demographic dramatic changes.The paper also tackles the political choices made in the seventies and eighties to understand it. In particular, it embraces the internal paralysis of the party faced with the challenges posed to all the European Communist Parties at this time, and its inability to deal with them. ; info:eu-repo/semantics/published