OBJECTIVE : The pulmonary artery (PA) in patients with pulmonary hypertension (PH) becomes dilated. We analyzed the postoperative changes of the main PA after lung transplantation (LuTx). METHODS : The subjects of this retrospective study were 68 LuTx recipients, divided into a PH group (n = 36) and a non-PH group (n = 32), based on preoperative right heart catheterization findings. The PA diameter was measured on chest computed tomography. We evaluated the correlation between the mean pulmonary arterial pressure (mPAP) and the main PA diameter and compared the main PA diameters before and 3 months after LuTx. RESULTS : The main PA diameter was significantly correlated with the mPAP (r = 0.423, P < 0.001). Preoperatively, the mean main PA diameter in the PH group was significantly greater than that in the non-PH group. However, by 3 months after LuTx, the main PA diameter in the PH group had decreased significantly from 32.4 ± 6.7 to 26.9 ± 4.8 mm (P < 0.001), while that in the non-PH group had decreased minimally from 28.3 ± 4.9 to 26.4 ± 4.6 mm (P < 0.001), resulting in no significant difference in postoperative main PA diameters between the two groups. CONCLUSIONS : The main PA diameter in recipients with PH was enlarged and correlated with the mPAP. The dilated main PA diameter in PH patients decreased shortly after LuTx.