Objective To observe the differences of peak expiratory flow (PEF), and serum eosinophil cationic protein (ECP) before and after Pulmicort aerosol inhalation for childhood asthma. Methods 113 asthmatic children treated with Pulmicort aerosol [(200～800) μg/d] for (3～12) months were studied. PEF was monitored with a peak flowmeter, and ECP was measured using fluoroimmunoassay (Pharmacia CAP system) before and after the treatment. Results PEF remarkably increased after inhalation therapy. Its percentage accounting for anticipant value after 3 m, 6 m, and 1 year ( 93.6 ± 5.4 , 93.0 ± 4.2 , 94.5 ± 4.5 ) had statistical significance compared with the percentage before inhalation therapy ( 70.4 ± 19.1 ) (P< 0.01 ). Serum ECP after the treatment [( 7.5 ± 2.7 ) μg/L] was significantly lower compared with ECP prior to inhalation [( 24.0 ± 17.1 ) μg/L] (P< 0.01 ). Conclusions Pulmicort aerosol appears to be an effective middle- and long-term therapy to treat and prevent childhood asthma because of its low incidence of side effects, its safety, and simplicity of use.