PURPOSE: The purpose of this study was to investigate the effects of the progressive walking-to-running technique (PWRT) in a child with spastic diplegic cerebral palsy (CP). DESIGN: A single case study with pre-/post-test. SUBJECT: An 11-year-old male, diagnosed with spastic diplegic CP. METHODS: The PWRT was provided for 60 minutes a day, 2 times a week for 12 weeks. Gross motor function tests, ultrasound imaging, hand-held dynamometer, and the Vicon motion capture system were used to determine motor function, muscle size and strength, and gait kinematics. RESULTS: Gross motor function was improved after the intervention. The size of right and left rectus femoris and tibialis anterior muscles in their contracted states were enhanced by 1.36, 5.09, 83.74, and 54.37%, respectively. Associated muscle strength was also increased by 58.8, 30.8, 28.0, and 118.2% in both rectus femoris and tibialis anterior muscles. Left stride length, walking speed, maximal flexion-extension angular excursion of the hip joint were enhanced by 95.7, 87.8, and 100.4% after PWRT, respectively. CONCLUSIONS: Our novel walking-running training paradigm was effective for restoring gait and running ability in a child with spastic diplegic CP.