The measurement of fractional exhaled nitric oxide (FeNO) is going to become more wide-spread as a noninvasive marker for diagnosing and controlling bronchial asthma. In Japan, both stationary and portable FeNO analyzers are now available. However, the difference between these analyzers has not been fully examined. Therefore, the aim of this study is to determine whether there is a difference between a stationary FeNO analyzer (NA623NP, CHEST inc. Tokyo, Japan) and a portable analyzer (NIOX MINO, Aerocrine, Solna, Sweden). One hundred subjects (17 non-treated asthma cases, 45 asthma cases treated with inhaled corticosteroids, 21 with other respiratory disorders, 17 healthy subjects) were enrolled in the study. All the subjects were non- or ex-smokers. There was a strong positive correlation between FeNO (CHEST) and FeNO (MINO) (r = 0.970, p < 0.001). However, when FeNO levels between FeNO (CHEST) and FeNO (MINO) were compared in all subjects and each subject group, the levels of FeNO (MINO) were significantly lower than those of FeNO (CHEST) (p < 0.05). Finally, the following conversion equation was calculated: FeNO (CHEST) = FeNO (MINO) x 1.278 + 3.065. From these results, the following conclusion was drawn: when FeNO is measured by different analyzers, there might be differences between devices. Therefore, the conversion equation could help clinicians and researchers to compare data obtainable by these two analyzers.