Left atrium (LA) gradually enlarges with the time course of atrial fibrillation (AF). The aim of this study was to examine whether the renin-angiotensin system (RAS) inhibitor could prevent LA remodelling in patients with chronic AF. Forty-one patients with chronic non-valvular AF were enrolled and divided into the following two groups: the RAS group taking an RAS inhibitor and the non-RAS group not taking it. We compared echocardiographic parameters including LA volume at the beginning and the end of follow-up. Percent change of these parameters was calculated from the value at the end of follow-up divided by the value at the beginning of follow-up. An enlargement of LA volume index and a decrease in LA expansion fraction was significantly prevented in the RAS group. Administration of RAS inhibitors was significantly associated with the prevention of increasing LA volume in multivariate analysis. RAS inhibitors may prevent structural and functional degradation of LA in chronic non-valvular AF.