Bibliographical studies have been done on plants that are used as analgesics in traditional medicine, and Mellissa officinalis or Lemon Balm (LB) that there are some evidence indicating for its application as analgesics or its probable analgesic effect was selected for evaluation of analgesic effect by tail-flick test in mice. After scientific identification, the leaves and flowered branches of LB were used for extraction by two methods, perculation and suxhelet. Male Albino mice, weighing 20-30 grams and aging 4-6 weeks, were utilized in 9-inserted groups. Methanolic perculated extract of LB with different doses 50, 75, 100, 200 and 300 mg/kg were injected intraperitoneally to experimental animals. Suxhelet extract was injected with a dose of 200 mg/kg. Aspirin 300 mg/kg and morphine 2.5 mg/kg were injected into the positive control groups and normal saline 10 ml/kg was injected into the negative control groups. The analgesic effect of the plant extracts and the drugs was measured for 120 in periods of 15, 30, 45, 60, 90 and 120 minutes after injection. The results show that LB extract has analgesic effect and the most analgesic effect was induced by 200 mg/kg of extract 15 minutes after injection. However, perculation extract has more analgesic effect than suxhelet extract. There are no significant differences between the analgesic effect of LB extract with morphine 2.5 mg/kg in the 15, 90 and 120 min and ASA 300 mg/kg in the 15, 60 and 90 min after injection.