Abstract: Objective To investigate the expression of eosinophil major basic protein (MBP) mRNA in bronchial asthma and explore its significance. Methods Peripheral blood eosinophil MBP mRNA levels were measured in 40 patients with asthma and 20 normal controls by semi-quantitative RT-PCR. The association of MBP mRNA levels with eosinophil count and pulmonary function was also analyzed. Results Compared with the normal control group, MBP mRNA level were significantly increased in asthma patients (0.37±0.11 vs 0.17±0.04, P<0.001), so was the eosinophil count (0.86±0.52 vs 0.21±0.10, P<0.001). MBP mRNA levels in patients with moderate persistent asthma (0.42±0.05) and those with severe persistent asthma (0.47±0.05) were significantly higher than those in patients with mild persistent asthma (0.25±0.06, P<0.001), and the difference in MBP mRNA levels between moderate persistent asthma patients and severe ones was also significant (P<0.05). Among the asthma patients, MBP mRNA levels showed an inverse correlation with pulmonary function (r=-0.749 0, P<0.001). Conclusion Increased MBP mRNA expression level may correlate with the severity of asthma. MBP may play an important role in the development of asthma.