OBJECTIVE: Duchenne muscular dystrophy (DMD) usually occurs prior to 3 years old. The value of serum creatine kinase changes with clinical progression and age in patients with DMD. This study aimed to investigate the regularity in the changes of serum creatine kinase activities in children with DMD. METHODS: Peripheral blood samples were obtained from 40 children with DMD (ranged from 3-14 years). Serum creatine kinase levels were assayed by kinetic UV test. RESULTS: Serum creatine kinase level in the 40 DMD patients (ranged from 2 595- 45 495 U/L) was remarkably higher than the reference value (35-174 U/L). The highest serum creatine kinase level (average: 27750-31173 U/L) was found in 3-5 years old patients. Afterwards, serum creatine kinase level decreased with clinical progression and age, with a yearly average rate of decline was 8.7%. CONCLUSIONS: Serum creatine kinase level reaches a peak between 3 and 5 years old and then reduces with increasing age in children with DMD. The characteristic changes of serum creatine kinase are suspected to reflect the rate of muscle decay.