Objective To investigate the level of fractional exhaled nitric oxide (FeNO) and its significance in patients with chronic asthmatic bronchitis or asthma during acute exacerbations. Methods A total of 100 outpatients, including 52 cases with acute exacerbation of chronic asthmatic bronchitis and 48 cases with acute exacerbation of asthma, were recruited from the Department of Respiratory Medicine in our hospital. FeNO level was measured using nitric oxide analyzer, and peripheral eosinophil ratios (EOS%) and lung functions were also detected at the same time. Comparative study was conducted for all the data obtained. Results FeNO level and EOS% in the chronic asthmatic bronchitis patients were significantly lower than those in the asthma patients (P < 0.01). Pulmonary function parameters in the chronic asthmatic bronchitis patients were significantly better than those in the asthma patients (P < 0.01). FeNO had no correlation with lung function parameters or EOS% in the chronic asthmatic bronchitis patients (P > 0.05). There was no correlation between FeNO and lung function parameters in the asthma patients (P > 0.05), however, there was a positive correlation between FeNO and EOS% (r = 0.626, P < 0.01). Conclusions FeNO, EOS% and lung function indexes may be used for distinguishing acute exacerbation of chronic asthmatic bronchitis from that of asthma.