When a non-photosensitive metallochromic pyridylazonaphtol chelate in polymer matrix was bombarded by an electron beam of medium energy (15 kV), its magenta color was turned to pale yellow. The decoloring reaction followed an first order reaction kinetics and was thought to be mainly due to an alteration of ligand. And it was effective in a matrix which liberated active acidic product by the bombardment. In the case of cuprous chelate (metal-to-ligand ratio was 1 : 1), the color of bombarded area was not so stable and the magenta recovered thermally. On the other hand in nickelous and zinc chelates (metal-to-ligand ratio was 1: 1), the decolored one was stable. The decoloration of the latter is thought to be useful in application as a positive type electron beam recording (EBR) medium. The recorded signal is expressed by an instant bleaching and medium is not sensitiv to light so that a fixing is not required for non-recorded area.