This study was designed to examine the effect of incentive spirometry in pulmonary rehabilitation of children with cerebral palsy. The incentive spirometer, a device that can help improve breathing and strengthen inspiratory muscles. If the patient assigned to training group, the subjects started to respiratory muscle strengthening exercise using incentive spirometry. The training was performed ten sessions daily, for 4 weeks. Respiratory function tests including forced vital capacity, forced expiratory volume in 1 second, Peak cough flow, maximal phonation time were compared before interventions and at the end of exercise.

Inclusion Criteria:

• male or female, 4 to 18 years
• patients who are committed to comply with protocol-required procedures
• GMFCS (Gross motor function classification system) level II, III, IV
• Stable medical condition in the investigator's opinion
• Acceptable chest radiologic result who has no evidence of pulmonary disease

Exclusion Criteria:

• Any uncontrolled clinically significant medical condition other than the one under study
• Patients with cognitive impairment who are unable to comply with protocol-required procedure
• Patients with presence or history of tracheostomy
• Patients who are taking medications that can affect respiratory function