Background: Infection is one of important risk factors related with acute exacerbation (AE) of asthma. Obesity increases the risk of developing asthma. Aim: To investigate isolated microbials and clinical significances in AEs between obese (BMI?25.0 kg/m²) and non-obese asthmatics. Methods: Total 407 patients (171 obese vs. 236 non-obese) were enrolled due to AE from 24 medical centers in Korea. Microbials were isolated from culture, RT-PCR and/or serologic test using specimens from lower respiratory tract. Results: Microbials were detected in 50.4% of subjects during AE, including virus (58%), bacteria (24%), and both (18%), respectively. Obese asthmatics were more common in female (77% vs 64%), had shorter history of asthma duration (7.9±8.4 vs 10.5±10.1 years), less common history of pulmonary tuberculosis (8.8% vs 17.4%), more common comorbidity of allergic rhinitis (48.5% vs 0.8%), lower incidence of Chlamydia pneumoniae (1.0% vs 7.6%), and more use of systemic corticosteroid (92% vs 88%) each with clinical significance, compared to non-obese group. Viral pathogens showed own unique patterns of occurrence. Conclusion: AE in obese asthmatics presented particular clinical characteristics. Isolated microbials in AE did not show significant differences between two groups except Chlamydia. Isolated microbial data may help to guide proper management in exacerbation of obese asthmatics in Korea.