In the present study, the main goal was to compare the effects of ionic copper versus copper nanoparticles in Enchytraeus albidus assessing the effect at the biomarker level, testing different concentrations and exposure times. Measured parameters were lipid peroxidation (LPO), total, reduced and oxidized glutathione content (TG, GSH and GSSG), the enzymatic activity of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), glutathione S-transferases (GSTs) and cholinesterases (ChEs). Results showed that both salt- and nano-copper caused oxidative stress and damage to E. albidus, as confirmed by LPO levels, and effects could be discriminated between the copper forms. Nevertheless and despite the visible discrimination between nano and the salt form (time and exposure dependent), there was no single or a set of biomarkers that provided the best discrimination.