Objective This study aimed to design a “ Gait enhancer” and investigate its effect on standing ability and Gait speed of children with cerebral palsy spastic diplegia. Materials & Methods A new gate trainer was designed based on Theo Johnson mechanism. Johnson's two separate movement chains were placed on either side of the gate trainer body and attached to the lower limbs by a foot plate. To investigate the effect of the designed device, a single-item experimental study with baseline design, treatment and maintenance (ABA) was performed on four children with available spastic diplegia cerebral palsy. These children received routine occupational therapy sessions. Results The designed “ Gait enhancer” increased standing ability and Gait speed scores in all subjects. Non-overlapping measures also indicated the improvement in both variables. Measured by Cohen’ s d, the effect size for standing ability were 1. 95, 2. 29, 1. 83, and 2. 3 for the child No. 1, 2, 3, and 4, respectively. Regarding walking speed, the effect size for these children, No. 1 to 4, were 1. 13, 3. 37, 2. 15, and 2. 21, respectively. Cohen’ s d values were greater than 0. 8, indicating the considerable effect of the intervention. Hedges’ g was also calculated due to the small sample size, which was greater than 0. 8 for all subjects in standing ability and Gait speed. Conclusion Following the use of Gait Enhancer along with conventional occupational therapy, we observed an increase in the ability to stand and walk at children with cerebral palsy. Findings showed that the change in standing ability and walking speed occurred more during the period of using the designed device than other stages, which could be a consequence of using Gait Enhancer along with routine occupational therapy sessions at this stage of the study. However, it should be noted that this study was only a single case study and to prove the effectiveness of this tool in children with cerebral palsy, it is necessary to conduct clinical trial studies.