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 <= 30.03mm, n= 53) and group 2 (ARD >30.03mm, 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.