The aims of this study were to assess the anesthetic vigor and histopathological effects of peppermint (Mentha piperita) essential oils in common carp (Cyprinus carpio). The total number of 70 fish with the average weight and length of 8.52±1.54 g and 8.47±1.16 cm were anesthetized by various concentrations of peppermint essential oils including 200, 250, 300, 350, 400, 450 and 500 ppm using the immersion method. The average amounts of temperature, pH and the hardness of water were 22±2˚C, 7 and 981 mg/L, respectively. The time taken to reach different stages of anesthesia, loss of equilibrium, twilight anesthesia, balance recovery and complete recovery were measured after exposure of fish to various concentrations of peppermint essential oils. In order to determine the effects of various concentrations of peppermint essential oils including 200, 300, 400 and 500 ppm at time 0 and 24 h, the tissue samples that were taken from the liver, kidney and gill of fish were examined by light microscopy. The results showed that the maximum and minimum time taken to reach complete anesthesia were observed after 10±5.11 and 73±16 seconds of exposure to 200 and 500 ppm of peppermint essential oils, respectively. The minimum time taken for recovery was 300±8.4 seconds which belonged to the treatment of 200 ppm peppermint essential oils. Moreover, the results showed that by increasing the concentration of anesthetic substance, the induction of anesthesia was faster and the time taken for complete recovery from anesthesia was increased. Histopathological studies showed that the optimum concentration of 200 ppm peppermint essential oils had no side effects. Therefore, this anesthetic concentration of peppermint essential oils can be safely used.