Materials and Methods: This interventional study is in a before-after design. Thirteen spastic diplegic cerebral palsy children with 8 to 12 years old were selected through students who studied in physical disabled schools in Tehran city and had the inclusion criteria. Patients used a static cock up c-bar splint (wrist in 10 degrees of extension and thumb in palmar abduction and opposition) for two months, 2 hours daily and 4-6 hours at night. In this study the Jebsen Taylor test was used to evaluate hand function, the Modified Ashworth Scale was used to assess spasticity of thumb, wrist and elbow, ROM of thumb, wrist and elbow were tested with goniometer and power grip was evaluated with dynamometer.  

 Results : Results showed a significant improvement in hand function (p<0.001), in wrist`s spasticity (p<0.001), elbow`s spasticity(p<0.008), palmar abduction of thumb spasticity (p<0.002), wrist`s ROM (p<0.001), Palmar abduction of thumb ROM(p<0.001) and power grip(p<0.001). The data did not show significant improvement on elbow`s joint ROM. 

Conclusion: Information from present research shows that using static cock up c-bar splint for 2 months, 2 hours a day and 4 to 6 hours nightly, can be an effective method to improve power grip, hand function, thumb, wrist and elbow spasticity and range of motion of thumb and wrist of spastic diplegic CP children.