To investigate clinical characteristics of postoperative supraciliary effusion (SCE) development following gonioscopy-assisted transluminal trabeculotomy (GATT) in patients with pseudoexfoliation glaucoma (PEXG). In this prospective and observational study, 64 eyes (64 patients) with PEXG were examined with spectral-domain optical coherence tomography (SD-OCT) after GATT over a 12-month follow-up. Outcomes were surgical success, intraocular pressure (IOP), best-corrected visual acuity (BCVA), number of antiglaucoma medications (AGM) and complications of the SCE (+) group with those of SCE (-) group. SCE was observed in 39 eyes (60.9%) within the first postoperative week. Probability of complete success was significantly higher in the SCE (+) group than in the SCE (-) group (25.6% vs. 16.0%, p = 0.009). IOP was significantly lower at postoperative first day in the SCE (+) group than in the SCE (-) group (p = 0.04), but it was similar thereafter during follow-up (p > 0.05). Postoperative BCVA did not show significant difference at the end of the follow-up (p > 0.05). Postoperative number of AGM was found to be significantly lower in the SCE (+) group compared to the SCE (-) group (p < 0.05). A significant IOP rise was observed after SCE resolution (p = 0.002). Presence of SCE accompanied with significantly lower IOP during the early postoperative period after GATT surgery for PEXG. SCE might have a favourable impact on postoperative AGM use. SCE can easily be examined by SD-OCT, and be used as a prognostic indicator.