Post-operative atrial fibrillation (AF) is a common and serious complication in patients undergoing aortic valve replacement (AVR). Speckle tracking echocardiography (STE) has recently enabled the quantification of longitudinal myocardial left atrial (LA) deformation dynamics. Our aim was to investigate LA preoperative mechanical function in patients undergoing AVR for aortic stenosis using STE and determine predictors of post-operative AF. 76 patients with aortic stenosis in sinus rhythm, undergoing AVR, were prospectively enrolled. Conventional echocardiographic parameters, and peak atrial longitudinal strain (PALS) were measured in all subjects the day before surgery. PALS values were obtained by averaging all segments in the 4- and 2-chamber views (global PALS). All patients received biological valve prostheses and a standard postoperative care. Postoperative AF occurred in 15 patients (19.7 %). On univariate analysis among all clinical and echocardiographic variables, global PALS showed the highest diagnostic accuracy (HR 6.55 p < 0.0001; AUC of 0.89) with a cut-off value <16.9 %, having sensitivity and specificity of 86 and 91 %, respectively, in predicting postoperative AF. LA volume indexed and E/e' ratio had lower diagnostic accuracy (AUC 0.76 and 0.51, respectively). On multivariate analysis global PALS remains a significant predictor of postoperative AF (p < 0.0001). STE analysis of LA myocardial deformation is considered a promising tool for the evaluation of LA subclinical dysfunction in patients undergoing AVR, giving a potentially better risk stratification for the occurrence of postoperative AF.