Background and Aim: Dental services in the clinics provides terms of exposure and infection to patients and staff to variety of bioaerosol that often Its origin are the patient's mouth. This study was done with aim of determine the air bacteriological contamination rate in one of the hospital's dentistry centers in Tehran-Iran.

Materials and Methods: In this cross sectional study, air sampling from selected parts was done using passive sampling method. Air bacteriological quality was determined with HPC testing, identification and enumeration of Staphylococcus aureus and Pseudomonas aeruginosa. The results were analyzed by SPSS16 software and t-test and ANOVA test.

Results and Conclusion: Bacteriological Quality %33/3 of air samples was evaluated at inappropriate status and more than the standard level (25CFU/plate/h). The counts of three air bacteriological indexes include HPC, s.aureus and
P. aeruginosa were respectively 43.8, 31.22 and 36.4 in terms of (CFU/plate /h). The highest air contamination was found in periodontal surgery. The mean numbers of bacteria in the air of case and control parts of studied center, shows a significant difference (p<0.05).This study showed that the air bacteriological quality was not acceptable level in dentistry-selected parts and threats the health of dentists and patient’s. So pollution load reduction and staff Health promotion, improve the local ventilation system, use of personal protective equipment (PPE) and air bacteriological quality continuous control, is necessary.