Background and Aim: Cerebral palsy is characterized by non-progressive abnormalities in the developing brain that create motor and postural deficits in the developing child. The most common feature of cerebral palsy is spasticity. In rehabilitation, orthotics have been used to prevent complications of spasticity and improve gait. There are some reports about effectiveness of tone-reducing AFO on decreasing tone in spastic cerebral palsy. The purpose of this study was to compare the effects of tone-reducing AFO on tone and gait between two groups of children with spastic diplegia. Materials and Methods: This randomized clinical trial was conducted on 30 children with spastic diplegia aged 2-8 years. They were assigned to either a control group (18 subjects) or a case group (12 subjects). All children were tested before and after 12 weeks of neurodevelopmental treatment 3 days a week by Modified Ashworth Scale and recording of the foot-print on a piece of paper fastened to the floor for the measurement of stride length, width and foot angle. Children in the case group wore the tone-reducing AFO approximately 6 hours a day. Results: A significant difference was found in muscle tone of the whole body between the two groups (p=0.025). Pretest and post-test difference of the plantar flexors and hamstrings in the case group were also significant (p=0.025, p=0.005). A significant difference was found in the right stride length (p=0.02) and the left stride length (p=0.03) between the two groups, but difference in stride width and foot angle were not significant. Conclusion: Tone-reducing AFO would significantly reduce tone of the whole body, the plantar flexors and hamstrings and increase stride length in spastic diplegic cerebral palsy.