Objective This study aimed to evaluate the three-dimensional changes in maxillary alveolar morphology after using modified NAM in patients with complete unilateral cleft lip and palate. Design This is a retrospective study. Setting The study was carried out in the dental hospital, Faculty of Dentistry of Naresuan University, Phitsanulok, which serves as a tertiary care center. Patients The population sample consisted of 19 patients with nonsyndromic complete unilateral cleft lip and palate. Intervention All patients received the modified NAM treatment based on the treatment protocol of the Naresuan University Cleft and Craniofacial Center, Thailand. Main Outcome Measure Dental models obtained at pre-treatment (T0) and post-treatment (T1) were scanned to construct the digital models. The maxillary digital models that showed dimensional changes between T0 and T1 were measured using a computer graphic software. Results The modified NAM resulted in a significant decrease in the anterior cleft width, posterior cleft width, and anterior arch width. Conversely, it caused a significant increase in the length of the lesser cleft segment and the greater segment rotation. However, the change in the height of both segments and posterior arch width was not found to be significant. Conclusions The modified NAM was an effective device for reducing the alveolar cleft width while improving the alignment of alveolar cleft segments.