Currently, in toxicology, the use of alternative models permits understanding the mechanisms of toxic actions at different levels of cell organization. In recent years, the fact that pesticides not only act against the target for which they are approved but on the whole ecosystem as well became unquestionable. Thus, the paramecium, as an alternative model, was chosen to test the effect of an acaricide (bifenazate) through measuring certain stress biomarkers. Four concentrations (10, 20, 40, and 80μM) were tested on aliquots of 50 ml of made-in-advance culture paramecia. The determination of enzyme biomarkers: catalase (CAT), ascorbate peroxidase (APX), and glutathione S-transferase (GST), revealed fluctuations in their activities, in conjunction with increasing both times and bifenazate concentration. In parallel, an induction of glutathione (GSH) after 24h of exposure and an increase in malondialdehyde (MDA) levels suggested a possible lipid peroxidation.