Background Microbes in the airway have been shown to be associated with the pathogenesis of asthma. The upper airway microbiome influences the dysbiosis of the lower airway microbiome. However, to date, the influence of upper airway microbiome for adult and elderly asthma has not been fully elucidated. Here, the metagenome of upper airway microbiome of young adults and elderly was analyzed to identify their association with adult asthma. Methods Nasopharyngeal swabs were collected from young adult and elderly asthma patients and non‐asthmatic subjects. The compositions and functional genes of airway microbiome were analyzed by high‐throughput sequencing. Results The composition of microbiota differed between young adult and elderly, and it was different between asthmatics and non‐asthmatics in each age group. Different bacteria were related to FEV1% predicted in each age group. Genes related to lysine degradation, N‐glycan biosynthesis, caprolactam degradation, and PPAR signaling pathway, which could be related to the reduction in inflammation and degradation of air pollutants, were higher in non‐asthmatics. Genes related to pentose phosphate pathway, lipopolysaccharide biosynthesis, flagella assembly, and bacterial chemotaxis—which may all be related to increased inflammation and colonization of pathogenic bacteria—were higher in young adult asthmatic patients. However, the functional genes of airway microbiome in elderly patients were not significantly different according to asthma morbidity. Conclusions These results suggest that the composition and function of upper airway microbiome could influence asthma pathogenesis, and the microbiome could play various roles depending on the age group. The upper airway microbiome was different between young adults and elderly, and their association with asthma was also different. The microbiome genes reducing airway inflammation and degrading air pollutants were lower in asthmatics, whereas genes enhancing inflammation and mucosal bacterial colonization were higher in asthmatics of young adults. The composition and function of upper airway microbiome could influence asthma pathogenesis, and the microbiome could play various roles depending on the age group.