Purpose The purpose of this study is to evaluate tumour vasculature with optical coherence tomography angiography (OCTA) in malignant choroidal melanoma (CM). Materials and methods Patients with unilateral CM were included in this cross-sectional observational clinical study. Applying OCTA systems operating at 840-nm wavelengths, eyes with CM were imaged. The primary main outcome measures were OCTA images, qualitative evaluation of macular and tumour vasculature, quantitative vascular density (VD), perfusion density (PD) and the foveal avascular zone disruption. Results The study included 11 patients with unilateral CM and contralateral unaffected eyes as the control group. Eyes of 11 patients with CM and contralateral unaffected eyes were imaged before brachytherapy and 5 patients were imaged post brachytherapy. CM is demonstrated dense, tortuous blood vessels, uneven thickness and relatively disorganised intratumoural vasculature. In 11 eyes with CM, the VD and PD in the macular area were significantly lower within affected eyes (131.333 +/- 27.807%, 3.152 +/- 0.714%, p < 0.0001) than in contralateral eyes (154.208 +/- 5.599%, 3.662 +/- 0.127%, p < 0.0001). The VD and PD in the tumour area (67.990 +/- 34.899%, 1.617 +/- 0.847%, p < 0.0001) were significantly lower when compared to the macular area of affected eyes (131.333 +/- 27.807%, 3.152 +/- 0.714%, p < 0.0001) and the macular area of contralateral eyes (154.208 +/- 5.599%, 3.662 +/- 0.127%, p < 0.0001). After radiation treatment, the VD and PD in five CM eyes (116.526 +/- 7.598%, 2.438 +/- 0.358%, p < 0.05) were significantly lower than before treatment (141.544 +/- 14.645%, 3.327 +/- 0.354%, p < 0.05). Tumour regression after radiation therapy for melanomas was associated with decreased vessel density. Conclusions OCTA can provide a dye-free, non-invasive, reliable method to monitor a variety of tumours, including CM for growth and vascularity. Upon OCTA, this could be helpful in evaluating the variety of tumour blood vessels before and after brachytherapy to judge the curative effect and whether the tumour recurred. Detection of the characteristic vascular features of CM by OCTA could make OCTA an assuring diagnostic modality to differentiate malignant lesions.