Background The diameter of the left atrium (LA) is a major index of prediction for LA fibrosis and ablation outcome in atrial fibrillation (AF)However, an unenlarged LA may not be associated with good results in some cases of AF ablation. Objective Exploring the characteristics and ablation prognosis of the patients with fibrotic but unenlarged LA Methods Patients with persistent fibrillation who underwent catheter ablation in our center were analyzed in this retrospective studyComprehensive low voltage mapped in LA is considered a fibrotic LAThe patients with fibrotic but unenlarged LA, normal LA, and fibrotic tissue with enlarged LA were included in Groups A, B, and C, respectivelyWe compared clinical features, electrophysiological findings, immediate ablation results, and follow-up outcomes in three groups. Results We enrolled 9 patients in Group A, 38 in Group B, and 12 in Group CThere were greater proportions of women, low ventricular rates, and high CHA2DS2-VASC scores in the patients with fibrotic LA (Groups A and C)At the end of procedure, all of the patients saw restored sinus rhythm, and the rate of sinus rhythm was lower in Groups A and C than in Group BAtrial-ventricular block and very-early-stage recurrence were more common in Group ASinus rhythm maintenance and LA reversion were rarer in Group A than in Group B or C. Conclusions A fibrotic but unenlarged LA was more likely to be seen in female with high CHADS2VA2S scoreIt indicated a poor prognosis for AF ablation.