Objectives: Previous studies have demonstrated that increased aortic root diameter (ARD) is frequently associated with increased cardiovascular (CV) events and is a predictor of stroke. Two-dimensional speckle tracking echocardiography (2D-STE) provides a better evaluation of left atrial (LA) functions. Left atrial mechanical dispersion is a useful predictor of new-onset atrial fibrillation (AF) independent of LA enlargement and dysfunction. We aimed to investigate the relationship between ARD and LA mechanical functions. Methods: The present study included 93 consecutive patients with hypertension and diabetes. The relationships between ARD and LA functions was evaluated. Results: Study population was divided into two groups according to the mean ARD values: group 1 (ARD ≤30.03 mm, n = 53) and group 2 (ARD >30.03 mm, n = 40). In group 2, age, LA max volume (vol), LA pre A vol, LA min vol, LA emptying fraction, LA active ejection fraction (EF), and LA expansion index were significantly higher compared to group 1. S‑LAs and SR-LAs (peak LA strain and strain rate, respectively, during ventricular systole) and S‑LAe and SR-LAe (peak early diastolic LA strain and strain rate, respectively) were significantly lower in group 2 compared to group 1. Age, LA max vol, LA pre A vol, LA min vol, LA emptying fraction, LA active EF, LA expansion index, S‑LAs, S‑LAe, SR-LAs, and SR-LAe were significantly associated with increased ARD. In multivariate logistic regression analysis, age, LA expansion index, and SR-LAe were independent predictors for ARD. Conclusion: Impaired LA mechanical functions determined by speckle tracking methods are related with increased ARD independent of LV diastolic dysfunction.