Background and aims: Complete isolation of the left atrial posterior wall (LAPW) is challenging owing to overlapping epicardial conduction. Peak frequency (PF) is a novel parameter that focuses on near- and far-field electrogram components. In this study, we aimed to determine whether transmural block completion is related to the ablation site PF. Methods: We analyzed 44 consecutive patients undergoing initial LAPW isolation between June 2023 and February 2024. Pre-LAPW isolation and PF maps were obtained using an HD-Grid catheter. In 17 of the 44 patients (Group-1), LAPW isolation was performed conventionally. In the remaining 27 patients (Group-2), PF-guided LAPW isolation was applied based on Group-1 results. Results: In Group-1, the left atrial roof and floor line success rates were 58.8% and 76.5%, respectively. The average PF value in the roof lines of patients with a completed block line was significantly higher than that of the remaining patients (286.6 ± 29.3 Hz vs. 236.1 ± 40.9 Hz, p = 0.012), but the floor lines were similar. In Group-2, relatively high PF values were targeted to achieve complete block of the left atrial roof and floor lines, following the results obtained in Group-1. The left atrial roof line success rates (92.6% vs. 58.8%, p = 0.007), total number of radiofrequency applications (22.7 ± 5.6 vs. 27.6 ± 8.5, p = 0.03), and procedural time (32.6 ± 18.3 vs. 47.9 ± 25.6 min, p = 0.03) differed between Group-1 and Group-2. Conclusion: Using a PF map for determining the optimal ablation line for LAPW isolation by radiofrequency catheter ablation is feasible.