Abstract : Separated Instruments have become a common problem nowadays during root canal treatment. Some previous studies have shown that olive oil has special properties to be used as a lubricant agent. No study has evaluated the effect of olive oil as a lubricant agent compared to EDTA in the removal of the separated instrument using ultrasonic tips. (2) Referred patients to the Department of Endodontics with the complication of separated instruments in the root canals of their lower first molars were screened. Two groups of patients (n=60) with separated instruments were included with equal numbers of straight and curved roots. Each group was exposed to the EDTA 17% or the olive oil during the application of ultrasonic tips according to the 'Terushi' technique with a 1:1 allocation ratio. The failure rate and the time required for removal of the separated instruments was calculated. Chi-square and student t tests were used to detect differences. In the curved canals groups, there were no significant differences between the EDTA and the olive oil in terms of the failure rate (13.4% and 7%, respectively; P≈1.000) and the mean removal time (2.50 and 2.22, respectively; P=0.665). In the straight canals groups, there were significant differences between the EDTA and the olive oil in terms of the failure rate (0% and 33.4%, respectively; P=0.028) and the mean operating time (1.40 and 2.10, respectively; P=0.042). The olive oil can be used as a lubricant agent in the removal of the separated instrument in the curved canals with a high success rate and an appropriate operating time. However, the EDTA performed better in the straight canals with higher success rate and shorter operating time compared to the olive oil.