Lactuca sativa (Lettuce) is a member of Compositae family. In folk medicine of Iran, the seeds of this plant were used for relieving of inflammation and osteodynia. In this study, anti-nociceptive and anti-inflammatory activities of a crude methanol/petroleum ether (70/30, v/v) extract of the seeds have been evaluated. The extract exhibited a time- and dose-dependent analgesic effect in formalin test and also a dose-dependent anti-inflammatory activity in a carrageenan model of inflammation. The extract had no analgesic effect in tail-flick test up to the highest dose used (6 g/kg). No abnormal behavior and lethality was observed by the extract up to 6 g/kg. Preliminary phytochemical analysis showed the presence of triterpenoids, saponins and simple phenols in the extract.