Background: Good trunk control is essential for higher developmental stages as the trunk is activated first when movement occurs, providing stability for the head and extremities. Purpose: To determine if neurodevelopmental treatment-based trunk control exercise (NDT-TCE) is effective in improving gross motor function and trunk control in children with developmental disabilities (DD). Materials and Methods: Twenty children with developmental disabilities were randomly assigned to the NDT-TCE (12 children) and control (8 children) groups. Results: After the intervention; the NDT-TCE group showed improvement in GMFM (Gross Motor Function Measure; except for the GMFM-E dimension) and SATCo scores. The control group showed improvement in GMFM-A; B; C; and total scores; as well as static and active control of SATCo. The NDT-TCE group had a significant improvement in the GMFM B dimension and total score compared to the control group. The NDT-TCE group showed a significant improvement in static and active control of SATCo compared to the control group, but there was no significant difference in reactive control. Conclusions: The NDT-TCE intervention specifically improved GMFM-B and trunk control scores. Therefore, NDT-TCE can be applied as a trunk-focused intervention for children with DD who have difficulty controlling their trunk.