Purpose The aim of this study was to determine the effects of expiratory musclebased respiratory strength training with visual feedback on pulmonary function, trunk stability, and gross motor function in children with spastic cerebral palsy. Methods Nineteen children with spastic cerebral palsy who consented to participate were randomly assigned to two groups. The experimental group underwent neurodevelopmental treatment for 20 minutes and respiratory strength training with visual feedback for 10 minutes. The control group underwent neurodevelopmental treatment for 30 minutes. The intervention was applied for 30 minutes, three times per week, for six weeks. We measured the forced vital capacity (FVC), forced expiratory volume at one second (FEV1), FEV1/FVC ratio, and peak expiratory flow (PEF) to evaluate pulmonary function. We also used the Trunk Impairment Scale (TIS) and Gross Motor Function Measure (GMFM) to evaluate trunk stability. Results There were significant improvements in FVC, FEV1, FEV1/FVC ratio, and PEF in the experimental group after training. Significant improvements in TIS and GMFM were observed only among the experimental group. Conclusion The study results suggest that children with spastic cerebral palsy can improve their pulmonary function, trunk stability, and gross motor function through expiratory musclebased respiratory strength training.