Introduction: Tanacetum sonbolii (Asteraceae) is an endemic species in Iran. In the present study, we examined the effects of Tanacetum sonbolii hydroalcoholic extract on the formalin test in mice. Methods: 126 Swiss albino mice weighing 230-280g were used as subjects. The formalin test was performed on two control groups (marked as intact and saline groups n = 6 in each group) and an experimental group. In all groups, the formalin test was recorded for 60 min after administration of extract and drugs in mice. Results: The results showed that Tanacetum sonbolii (150 and 300 mg/kg) produced significant antinociception in phase 2. In addition, different doses of Tanacetum sonbolii extract (600, 900 and 1200 mg/kg) also induced antinociceptive effects in phase1 and phase 2. On the other hand, morphine could induce antinociception in a dose-dependent manner. Diclofenac (10 mg/kg) failed to affect the pain scores compared to Tanacetum sonbolii (300 mg/kg) group. Discussion: It seems that administration of hydroalcoholic extract of Tanacetum sonbolii has the potential to relieve pain through both central and peripheral mechanisms in persistent inflammatory nociception.