Background: Head and neck infections happen due to different reasons and different microorganisms are responsible for them. These infections can be treated with various antibiotics. The purpose of this study was to specify most frequent etiology of infection, dominant bacterial species and most effective antibiotic in patients with head and neck infections who referred to Shahid Rajaee hospital of Shiraz.Methods: This study has been carried out in cross-sectional pattern from 2019-May to 2020-Oct in Oral & Maxillofacial Ward of Rajaee Hospital of Shiraz. Consent to access data and archive files was taken from the ethics committee of Shiraz University of Medical Sciences. Age, sex, etiology of infection, bacterial species, sensitivity or resistance reaction to Antibiotics and most frequently used antibiotic in patients who referred to this ward between 1392-Apr to 1398-Mar were collected on the basis of laboratory’s results. Data were analyzed with Chi-Square test.Results: statistical analysis showed that, 56 of patients were men (54.9%) and 46 were women (45.1%). The average of age was 38+/−17 and the minimum age was 6 and maximum age was 73. The most frequent etiology was odontogenic infections. Moreover, there was no statistically significant relationship between etiology and bacterial species (p-value=0.38) and Cefazolin had the most frequency in odontogenic infection group. Top three frequent bacterial species were respectively: Staphylococcus DNase & Coagulase Negative, Enterococci Sp., Streptococci Viridians and Klebsiella Sp. . There was no statistically significant relationship between bacterial species and sex (p-value=0.55). 94 (48.7 %) of bacterial species had Sensitive reaction to antibiotics. 21 (10.9 %) of them had Intermediate reactionand 78 (40%) of them had Resistant reaction and Cefazolin had the most frequency in sensitive group.Conclusion: The dominant bacterial species in head and neck infections are Staphylococcus DNase & coagulase negative. And, Cefazolin had the most sensitive reaction in odontogenic infections.