This study aimed to investigate changes in choroidal thickness after pars plana vitrectomy (PPV) with and without air tamponade in patients with idiopathic epiretinal membrane (ERM). We retrospectively reviewed 61 patients with ERM who underwent a 25-gauge transconjunctival sutureless PPV. The patients were divided into two groups: the air tamponade group (30 eyes) and the nontamponade group (31 eyes). Subfoveal choroidal thickness (SFCT) was analyzed over 12 months. No significant differences were seen between the two groups at baseline. For all patients, the SFCT was significantly thicker at 1 month after surgery and significantly thinner at 6 and 12 months after surgery than preoperative values. In the subgroup analysis, there was no significant difference in SFCT 3 months after surgery compared with the preoperative values in both groups, but SFCT was significantly lower 6 months after surgery in both groups. In conclusion, our results showed that choroidal thickness temporarily increased after surgery and then gradually decreased until 12 months after the PPV for ERM.