Stevia (Stevia rebaudiana Bertoni.) leaves have been used in many countries. It called as sweet herb. Stevia leaves have been used as either a sweetener or as a medicinal plant. The aim of this work was to study its mutagenic and antimutagenic potentiality using bacterial assays (prophage induction and transduction). The results showed that the survival percentages of bacterial cells tested with stevia extract at concentration 10% did not changed greatly. The obtained results showed a minor increase in prophage F₁₁₆ induction assay, wherease pfu/ml ranged from 1.58 up to 2.34 × 10⁴ as a result of using the concentrations from 0.00 up to 20.00% respectively. When applying the Heinemann (1971) equation on transduction analysis, it was noted that the increase than control ranged from 1.03 up to 1.34 folds only when 20% of stevia extract was used. In order to assay antimutagenic response of stevia to a mutagenic compound (EMS), whereas mutagenic index (MI) dropped from 12.06 at 20.00% of EMS up to 3.36 when 10% of stevia extract was added. The results proved that stevia leaves ethanol extract has no mutagenic activity and it has an antimutagenic activity.