Bunium persicum (Boiss.) is an economically important medicinal plant growing wild in arid regions in Iran. The essential oil of B. persicum (EOBP) was extracted using hydrodistillation. A total of eighteen compounds, representing 96.14 % of the oil was identified by gas chromatography/mass spectrometry (GC/MS).The main compounds were cuminaldehyde (23.04 %), gamma-terpinene (14.48 %), trans-3-Caren-2-ol (12.51 %), acetic acid (10.90 %) and 1,3,8 -p- menthatriene (7.89 %). The effects of 0.1 to 1000 g mL-1 EOBP on ruminal and abomasal smooth muscle of twenty-four healthy sheep and ileum preparations of six rats were assessed in vitro. Ruminal preparations showed relaxation (P < 0.05) when exposed to 100 - 1000 g mL-1 concentrations of EOBP. In the isolated abomasal preparations, EOBP (0.1 - 1 g mL-1) represented a weak spasmogenic effect followed by relaxation. The spontaneous contraction of abomasal smooth muscles was completely abolished with a high dose (1000 g mL-1) of EOBP. Five-minute incubation with EOBP, significantly (P < 0.05) inhibited Ach-induced contraction in higher doses on both tissues. In contrast, rat ileum only showed dose-dependent relaxation effect, and pre-incubated tissues with EOBP, decreased the Ach-induced contraction. The data indicated that the plant contained spasmogenic and spasmolitic constituents. The results also showed that the EOBP profoundly alters gastrointestinal smooth muscle contraction in a dose-dependent and tissue-specific manner.