Abstract: The aim of the present study was to determine the causative agents of osteomyelitis and specifying their antibiotic resistance pattern in patients referred to pediatrics ward of Imam Khomeini Hospital. This study has been performed in Tehran during January to December 2006. In this study, synovial fluid was taken from 90 patients who referred to pediatrics ward of Imam Khomeini. Samples were examined by direct test, culture and biochemical tests. In next step, antibiogram by disk diffusion method (Kirby-Bauer Test) was established on each positive sample and finally, the results were analyzed. Of 90 examined samples, 27 bacterial cases were isolated; Staphylococcus aureus with 55.9% was the most epidemic agent and Klebsiella sp., coagulase negative Staphylococci, Streptococcus pneumoniae and Enterobacter sp. were the next common agents, respectively. However, it was revealed that more than 40% Staphylococcus aureus are sensitivity to Vancomycin, Gentamicin, Sulfamethoxazole and Erythromycin and most of gram negative Rods isolated of were sensitivity to Amikacin, Ampicillin and Cephalothin (50-100%). The most of bacteria (Staphylococcus aureus, coagulase negative Staphylococci, Streptococcus pneumoniae and Enterobacter sp.) were sensitive to Vancomycin, gentamicin and Cephalothin. Similar to previous results, it was proved either in our study that Staphylococcus aureus is the main agent of osteomyelitis and gram negative bacteria with coagulase negative Staphylococci and Streptococci are other agents. Also, it was observed that the most isolated bacteria had high antibiotic resistance to common drugs.