Background and Objective: There are many chemical, physical and biological hazards which are threatening the dentists' health. In this study we assessed the effect of noise on Zanjan dentists hearing loss as one of the dentistry physical hazards. Materials and Methods: This cross sectional study was performed on all zanjan dentists in 2006-7. All dentists were examined by audiometer (CA76 and AC40). The exclusion criteria were hearing accidents and diseases. The data were statistically analyzed by T test ( =0.05). Results: Noise induced hearing loss was observed in most cases. Left ear was more susceptible than right ear. The men had more hearing loss than the women. (P value on Freq 8000 HZ= 0.001). Deutists with seniority of 10 years and over had more hearing loss than who have seniority of less than 10 years (P value on Freq 8000 HZ= 0.004). The dentists in the age of 40 years old and over had more hearing loss than the ages below 40 year (P value on freq 8000 HZ in the left ear = 0.007, in the right ear = 0.019). Left ear had more hearing loss than right ear. Noise induced hearing loss in extra–speech frequencies was more than speech frequencies. The noise frequency of dental equipments was between 70 to 105 db. Conclusion: Noise induced hearing loss which has threatened the dentists' health is an incurable problem that must be prevented. Regular audiometric exam, use of hearing protection devices and also the occupational health regulations must be implemented for dentists in order to reduce the risk of noise induced hearing loss.