Background: To evaluate the peripheral vitreoretinal abnormality (PVA) and its correlation with the risk of malignant glaucoma (MG) in nanophthalmos with secondary angle closure glaucoma (NSACG). Methods: This prospective case series included 47 NSACG eyes with axial length (AL) < 21 mm from 25 patients. PVA was defined as a hyperreflective echo at the peripheral vitreoretinal region under ultrasound biomicroscopy (UBM). Eyes were categorised into two groups based on the presence (PVA group) or absence (NPVA group) of PVA. AL, lens thickness (LT), radius of corneal curvature (K1: flat, K2: steep), and corneal cylinder degree (CYL) were measured by IOL-Master. Anterior chamber depth (ACD), lens vault (LV), corneal limbus thickness (CLT), trabecular-ciliary processes distance (TCPD) and angle (TCPA), and peripheral iris thickness (PIT) were measured by UBM. MG incidence was recorded during a minimum 2-year follow-up. Results: PVA was detected in 29 eyes(62%) from 16 patients (64%). PVA eyes had shorter AL, TCPD, TCPA and larger PIT, LT, LV, CLT, K1, K2 compared to NPVA eyes (all P < 0.05). Thirteen eyes (45%) in the PVA group developed MG postoperatively vs none in the NPVA group (P < 0.05). Logistic regression analysis, adjusted for AL, identified older age, greater angle occlusion, larger K2, higher CYL, thicker LT and CLT as significant risk factors for MG (all P < 0.05). Conclusions: We first reported PVA under UBM in NSACG eyes, which may partially explain their anatomical predisposition to advanced ACG and MG, and aid in the management of these eyes.