Speaking at an event of the German Film Academy, Merkel said she had never kept the memberships a secret, but had never been asked about them, The Local.se reported Monday.
Merkel, head of the conservative Christian Democratic Union, revealed she had been a member of the Free German Trade Union Federation (FDGB) and the Society for German-Soviet Friendship.
The vast majority of East German workers and employees were members of the FDGB, which was considered a basic component of the East German government's power structure. The Society for German-Society Friendship was a propaganda tool for promoting cooperation between East Germany and the Soviet Union.
Scrutiny of Merkel's past has been renewed by a new biography that questions whether she was a secretary for Free German Youth (FDJ), the official socialist youth organization of East Germany, then called the German Democratic Republic.
Merkel has said in the past she joined the FDJ only for "community reasons."
Sunday night, she said, "I only have my memory to rely on. If something else comes out now I can live with that."