Abstract: In this research, hydroalcoholic extract obtained from the aerial parts of Marrubium parviflorum (Lamiaceae) was subjected to evaluation of analgesic effects using formalin test at the doses of 50, 100 and 200 mg kg-1 in mice. Duration of licking and biting time (min) of the injected paw was recorded at 5 min intervals for 40 min after formalin injection as a pain index. Results of study showed that the dose of 100 mg kg-1 of the extract decreased duration of licking and biting time between 15 and 40 min, but this effect was not statistically significant (p>0.05), while the dose of 200 mg kg-1 of extract showed significant analgesic effects (p<0.05) in the chronic phase (15-40 min) of formalin induced pain that this analgesic effect was equal to morphine. Considering that chronic phase of formalin induced pain is a secondary response to formalin induced inflammation, results of study introduce the M. parviflorum as a valuable analgesic herbal medicine that can be used in treatment of inflammatory painful disease. It is possible to assume that phytochemical contents of M. parviflorum reduce inflammatory pain by inhibiting the formation of inflammatory mediators such as prostaglandins followed by inhibiting COX-II enzyme.