Aim To investigate the relationship between red cell distribution width (RDW) and left atrial diameter (LAD) in patients with atrial tachyarrhythmia. Methods This retrospective study included 460 patients with atrial tachyarrhythmia from October 2013 to August 2014. The patients’ RDW and echocardiography results were collected to investigate the relationship between RDW and LAD. Results Patients were divided into three groups by sorting RDW values in an ascending order. RDW value, LAD value had significant difference among these groups (P＜0.05). With increased RDW, the LAD value gradually elevated. Pearson correlation analysis was applied to control other influencing factors, and multiple correlation analysis showed that LAD was positively correlated with RDW (r＝0.297, P＝0.000). With atrial tachyarrhythmia (Kleiger class 1～3＝0, Kleiger class 4～6＝1) as a dependent variable, binary classification Logistic multivariate regression analysis showed that RDW (OR＝1.215) and LAD (OR＝1.024) were risk factors for atrial tachyarrhythmia. Conclusion RDW is independently correlated with LAD in patients with atrial tachyarrhythmia.