Solvent extracts of ginger, the rhizome of Zingiber officinale Roscoe (Zingiberaceae), have been extensively studied for their pharmacological activities in smooth muscles. However, the effects of ginger essential oil on smooth muscle contractility have not been elucidated. The aims of the study were to investigate the effects of ginger oil on rat myometrial contractility. We particularly examined the effects on phasic contractions arising either spontaneously or with PGF_2α stimulation. Ginger oil was obtained by hydrodistillation and its constituents analyzed using gas chromatography and mass spectrometry. Rats were humanely killed by asphyxiation with CO₂, and longitudinal uterine smooth muscles were isolated. Isometric force was measured and the effects of ginger oil studied. It was found that citral was the main constituent of ginger oil (24%). Ginger oil inhibited spontaneous contractions with an IC₅₀ of 50 μL/100 mL (10-150 μL/100 mL). The PGF_2α-induced contractions were also significantly reduced by ginger oil. Increases in external calcium concentration completely reversed the relaxant effects of ginger oil. This was the case for both spontaneous and PGF_2α-induced contractions. The effects of ginger oil were indistinguishable from those of pure citral. In conclusion, ginger oil is a potent inhibitor of phasic activity in rat uterus, irrespective of how it was produced. Our data suggest that the effects are largely due to citral, and could be via inhibition of L-type Ca channels.