Introduction: An accurate evaluation of atrial septal defect (ASD) is important for the success of interventional treatment. Cardiac computed tomography (CT) has unique advantages for ASD assessment, although transesophageal echocardiography (TEE) remains the accepted method. Objective: This study aimed to evaluate the safety and feasibility of transcatheter closure of ASD with cardiac CT sizing but without TEE measurement. Methods: Among 134 patients undergoing transcatheter closure, 13 underwent TEE in addition to a cardiac CT examination, and 121 underwent only cardiac CT. Propensity score matching was used to analyze the outcomes of the groups treated with (group 1) or without (group 2) TEE examinations. The success rate and complications among the 121 ASD patients with only cardiac CT sizing were recorded and analyzed. The maximal diameters of the defects remeasured on CT images were compared to the echocardiography results and correlated with the device size by Student t test and Pearson’s linear regression analysis, respectively. Results: No significant differences ( p > 0.05) were found between groups 1 and 2 in the success rate, complications, or ratio of the device size to the maximum diameter of the defect measured by cardiac CT. In group 1, the maximum diameters of the ASD derived from cardiac CT and TEE were comparable (22.08 ± 9.68 vs. 21.50 ± 10.24; p = 0.351). The success rate among the 121 patients who underwent transcatheter closure with only cardiac CT sizing was 99.2%; however, within 1 month of follow-up, 2 patients had arrhythmia, 1 patient had residual shunting, 1 patient had an infection, and 1 patient had a hematoma, but all patients recovered within a short time. Conclusions: Cardiac CT seems to be comparable to TEE in the assessment of ASD, and transcatheter closure of ASD based on CT sizing alone is safe and feasible.