Essential oils that were extracted by steam distillation from Origanum onites L. from northwest Turkey were analyzed using an Agilent GC-MSD system. Carvacrol was the major component (64.3%) of the oil. Both pure commercial carvacrol and essential oil at concentrations of 1.5%, 3.2%, 6.25%, 12.5%, 25%, 50%, and 100% (v/v) were tested for their effects against engorging Rhipicephalus turanicus, which were collected from cattle breeding in the region. Pure carvacrol killed all the ticks following 6 h of exposure, while 25% and higher concentrations of the oil were completely effective in killing the ticks by the 24th-hour post-treatment (p < 0.05). The concentrations of 6.25% and 12.5% killed all the ticks by day 2. Lethal concentrations for 50% (LC(50)) and 90% (LC(90)) of 2.34% and 7.12%, respectively, were detected 24 h post-treatment. These findings indicate that the essential oil of O. onites L. has potential to be utilized at reasonable concentrations to control tick infestations.