Background: The damaging effect of exposure to loud noise on the structures of internal ear has been studied from many years ago. The effect of drill-generated noise on the non-operated ear is one of the problems that are less discussed. This study aims to evaluate the hearing loss that occurs in the non-operated ear in patients who undergo mastoidectomy by use of PTA (pure tone audiometery) and DPOAE (distortion product otoacoustic emission).Materials and Methods: In this descriptive- analytic study, 49 patients who underwent mastoidectomy in Amir-Alam and Iman Khomeini hospitals, were evaluated for noise trauma generated by drilling on the non-operated ear. Patients were between 9-55 years old (mean age= 29) and they consisted of 25 males and 24 females. The patient's preoperative state were measured by PTA and DPOAE on the opposite ear also the postoperative state were re-evaluated by PTA and DPOAE.Results: As a result, in 4 cases a significant change in PTA thresholds were observed, while two of them showed recovery after one month. Seven cases showed significant change in DPOAE amplitudes, of whom five cases recovered later.Conclusion: In conclusion, the drill-induced hearing loss on the non-operated ear occurs in a few patients and it is often reversible.