Objective : The purpose of this study was to investigate the effect of the environmental enrichment therapy (EET) program on the task performance and sensory processing of children with delayed development. Methods : This study was conducted with a single-subject ABA research design for two children with developmental delay findings, and intervention was conducted 7 times a week for 4 weeks. Both children confirmed changes in task performance and sensory processing after intervention. Results : After intervention, task performance improved from an average of 200% to a maximum of 354% compared to the baseline period, and the score in the sensory processing area, which affects tactile processing, emotional response, and activity level, was improved to the normal category. Conclusion : Through this study, it was confirmed that the EET program was effective in performing tasks and sensory processing for children with developmental delays, and its usefulness was confirmed as a program that can be implemented at home.