ABSTRACT Background The efficacy of cryoballoon ablation (CBA) using a 28‐mm or 31‐mm cryoballoon for isolating the left common pulmonary vein (LCPV) remains poorly established. We aimed to evaluate procedural outcomes and long‐term follow‐up data of CBA for the LCPV using either POLARx with a fixed 28‐mm cryoballoon or POLARx FIT with a size‐adjustable 28‐mm or 31‐mm cryoballoon. Methods Patients with LCPV who underwent CBA for atrial fibrillation using POLARx or POLARx FIT between January 2022 and April 2024 were retrospectively analyzed. Procedural outcomes and long‐term follow‐up data were compared between the POLARx and POLARx FIT groups. Results Fifty‐one patients (32 males [62.7%]; mean age, 66 ± 11.6 years) were analyzed. The POLARx group included 23 patients, and the POLARx FIT group included 28 patients. First‐freeze pulmonary vein isolation (PVI) success was 1 (4.3%) versus 8 (28.6%) ( p = 0.03), and radiofrequency touch‐up ablation was required in 2 (8.7%) versus 0 patients ( p = 0.2) in the POLARx and POLARx FIT groups, respectively. Nadir temperature was −53.6° ± 4.7°C versus −54.7° ± 5.6°C ( p = 0.45); the number of applications was 3.2 ± 1 versus 2.3 ± 0.9 ( p < 0.01); and total freezing time was 520.9 ± 164 s versus 377.7 ± 129.9 s ( p < 0.01) for the POLARx and POLARx FIT groups, respectively. A single gastric hypomotility case was observed in the POLARx FIT group. The 1‐year arrhythmia‐free survival rates were 81.8% and 78.7% for the POLARx and POLARx FIT groups, respectively ( p = 0.96). Conclusions POLARx FIT was useful for LCPV isolation, with a higher first‐freeze PVI success rate, fewer applications, and shorter total freezing time compared to POLARx.