Objective: I. To assess the frequency with which influenza, adenovirus and respiratory syncytial virus (RSV) in patients under jive years of age with asthma. 2. To determine the contribution of RSV, Adenvirus, influenza vớu A, B to acute episode ũ bronchial asthma in children. Subject and method: Nasopharyngeal aspirate from children under aged 5 years with asthma were testedfor RSV, Adenovirus, Influenz.a A and B by PCR and realtimePCR. Results and conclusion: Viral identification was positive in 83.78 percent in chindren under 5 years of age. Among them the rate o[ andenovirus, RSV, influenza virus A. B were 21.62 percent. 38.88 percent, 72.97 percent and 0 percent respectively. RSVand influenza A affected the severity of bronchial asthma: influenza A virus accounted for 81.48 percent and RSVaccountedfor 92.86 percent (p = 0.001, OR = 15.74) in these children with severity of bronchial asthma.