Abstract Cleft lip and palate are the most common congenital malformations in the craniofacial region, occurring at a rate of 1:700 births in Brazil. These conditions lead to functional impacts on patients, such as changes in breathing, teeth, speech, chewing, swallowing and sucking. Treatment begins with primary surgeries, including lip and palate repair, which aim to reconstruct the soft tissues. Secondary alveolar bone grafting (SABG) reconstructs the bone defect in the cleft region, with the main goal of supplying bone tissue to the cleft region and restore the continuity of the alveolar process. Objective: To measure the changes in cross-sectional areas (CSAs) and nasal volume in patients and their impact on the nasal cavity (NC) in the two-month postoperative period (PO2M). Methodology: This study included 15 patients with complete unilateral cleft lip and palate (U/CLP) indicated for alveolar bone grafting (ABG). Cone beam computed tomography scans obtained prior to SABG and at PO2M were compared. Nasal volumes and CSAs were measured by marking the masks delimiting the nasal cavity on CT scans using Mimics™ software. Results: NC volumes (total, right and left sides) were statistically lower at PO2M in patients with left-sided UCLP. In right-sided UCLP, these volumes were only significant for the total NC and left NC. The CSAs of the internal nasal valve in both groups showed significantly lower values compared to the preoperative period (p≤0.05). Conclusion: In the short term, alveolar bone graft surgery reduces the volume of nasal cavities and the cross-sectional areas of the right and left internal nasal valve as a whole, not only the cleft area where the graft material was placed. 1700 1 700 1:70 Brazil breathing teeth speech chewing sucking surgeries repair tissues (SABG process Objective crosssectional cross sectional (CSAs (NC twomonth two month PO2M. POM . PO M (PO2M) Methodology U/CLP UCLP U CLP (U/CLP ABG. ABG (ABG) Mimics software Results total, (total sides leftsided sided rightsided p≤0.05. p005 p p≤0.05 0 05 (p≤0.05) Conclusion term whole placed 170 70 1:7 (PO2M (ABG p00 p≤0.0 (p≤0.05 17 7 1: p0 p≤0. (p≤0.0 p≤0 (p≤0. p≤ (p≤0 (p≤ (p